diff --git a/crates/fj-core/src/algorithms/approx/curve.rs b/crates/fj-core/src/algorithms/approx/curve.rs
index d3fa3fc31..b0a658a2a 100644
--- a/crates/fj-core/src/algorithms/approx/curve.rs
+++ b/crates/fj-core/src/algorithms/approx/curve.rs
@@ -181,12 +181,12 @@ mod tests {
         geometry::{CurveBoundary, GlobalPath, SurfaceGeometry, SurfacePath},
         objects::{Curve, Surface},
         operations::insert::Insert,
-        Instance,
+        Core,
     };
 
     #[test]
     fn approx_line_on_flat_surface() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let curve = Curve::new().insert(&mut core);
         let (surface_path, boundary) =
@@ -203,7 +203,7 @@ mod tests {
 
     #[test]
     fn approx_line_on_curved_surface_but_not_along_curve() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let curve = Curve::new().insert(&mut core);
         let (surface_path, boundary) =
@@ -223,7 +223,7 @@ mod tests {
 
     #[test]
     fn approx_line_on_curved_surface_along_curve() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let global_path = GlobalPath::circle_from_radius(1.);
         let curve = Curve::new().insert(&mut core);
@@ -257,7 +257,7 @@ mod tests {
 
     #[test]
     fn approx_circle_on_flat_surface() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let curve = Curve::new().insert(&mut core);
         let surface_path =
diff --git a/crates/fj-core/src/algorithms/intersect/curve_edge.rs b/crates/fj-core/src/algorithms/intersect/curve_edge.rs
index 7b73d57c8..91a1129c6 100644
--- a/crates/fj-core/src/algorithms/intersect/curve_edge.rs
+++ b/crates/fj-core/src/algorithms/intersect/curve_edge.rs
@@ -73,14 +73,14 @@ mod tests {
 
     use crate::{
         geometry::SurfacePath, objects::HalfEdge,
-        operations::build::BuildHalfEdge, Instance,
+        operations::build::BuildHalfEdge, Core,
     };
 
     use super::CurveEdgeIntersection;
 
     #[test]
     fn compute_edge_in_front_of_curve_origin() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let path = SurfacePath::u_axis();
         let edge =
@@ -98,7 +98,7 @@ mod tests {
 
     #[test]
     fn compute_edge_behind_curve_origin() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let path = SurfacePath::u_axis();
         let edge =
@@ -116,7 +116,7 @@ mod tests {
 
     #[test]
     fn compute_edge_parallel_to_curve() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let path = SurfacePath::u_axis();
         let edge =
@@ -129,7 +129,7 @@ mod tests {
 
     #[test]
     fn compute_edge_on_curve() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let path = SurfacePath::u_axis();
         let edge =
diff --git a/crates/fj-core/src/algorithms/intersect/curve_face.rs b/crates/fj-core/src/algorithms/intersect/curve_face.rs
index dc5472a42..8d2776e25 100644
--- a/crates/fj-core/src/algorithms/intersect/curve_face.rs
+++ b/crates/fj-core/src/algorithms/intersect/curve_face.rs
@@ -159,14 +159,14 @@ mod tests {
             build::{BuildCycle, BuildFace},
             update::{UpdateFace, UpdateRegion},
         },
-        Instance,
+        Core,
     };
 
     use super::CurveFaceIntersection;
 
     #[test]
     fn compute() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let (path, _) = SurfacePath::line_from_points([[-3., 0.], [-2., 0.]]);
 
diff --git a/crates/fj-core/src/algorithms/intersect/face_face.rs b/crates/fj-core/src/algorithms/intersect/face_face.rs
index da459655f..eb60b7ebd 100644
--- a/crates/fj-core/src/algorithms/intersect/face_face.rs
+++ b/crates/fj-core/src/algorithms/intersect/face_face.rs
@@ -68,14 +68,14 @@ mod tests {
             build::{BuildCycle, BuildFace},
             update::{UpdateFace, UpdateRegion},
         },
-        Instance,
+        Core,
     };
 
     use super::FaceFaceIntersection;
 
     #[test]
     fn compute_no_intersection() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         #[rustfmt::skip]
         let points = [
@@ -106,7 +106,7 @@ mod tests {
 
     #[test]
     fn compute_one_intersection() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         #[rustfmt::skip]
         let points = [
diff --git a/crates/fj-core/src/algorithms/intersect/face_point.rs b/crates/fj-core/src/algorithms/intersect/face_point.rs
index 38a98a1a2..a634dc6dd 100644
--- a/crates/fj-core/src/algorithms/intersect/face_point.rs
+++ b/crates/fj-core/src/algorithms/intersect/face_point.rs
@@ -140,12 +140,12 @@ mod tests {
             build::{BuildCycle, BuildFace},
             update::{UpdateFace, UpdateRegion},
         },
-        Instance,
+        Core,
     };
 
     #[test]
     fn point_is_outside_face() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -171,7 +171,7 @@ mod tests {
 
     #[test]
     fn ray_hits_vertex_while_passing_outside() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -200,7 +200,7 @@ mod tests {
 
     #[test]
     fn ray_hits_vertex_at_cycle_seam() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -229,7 +229,7 @@ mod tests {
 
     #[test]
     fn ray_hits_vertex_while_staying_inside() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -258,7 +258,7 @@ mod tests {
 
     #[test]
     fn ray_hits_parallel_edge_and_leaves_face_at_vertex() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -287,7 +287,7 @@ mod tests {
 
     #[test]
     fn ray_hits_parallel_edge_and_does_not_leave_face_there() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -322,7 +322,7 @@ mod tests {
 
     #[test]
     fn point_is_coincident_with_edge() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
@@ -359,7 +359,7 @@ mod tests {
 
     #[test]
     fn point_is_coincident_with_vertex() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let face =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
diff --git a/crates/fj-core/src/algorithms/intersect/ray_face.rs b/crates/fj-core/src/algorithms/intersect/ray_face.rs
index 4b62b1f03..23e70a385 100644
--- a/crates/fj-core/src/algorithms/intersect/ray_face.rs
+++ b/crates/fj-core/src/algorithms/intersect/ray_face.rs
@@ -154,12 +154,12 @@ mod tests {
             transform::TransformObject,
             update::{UpdateFace, UpdateRegion},
         },
-        Instance,
+        Core,
     };
 
     #[test]
     fn ray_misses_whole_surface() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -191,7 +191,7 @@ mod tests {
 
     #[test]
     fn ray_hits_face() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -226,7 +226,7 @@ mod tests {
 
     #[test]
     fn ray_hits_surface_but_misses_face() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -258,7 +258,7 @@ mod tests {
 
     #[test]
     fn ray_hits_edge() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -300,7 +300,7 @@ mod tests {
 
     #[test]
     fn ray_hits_vertex() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -343,7 +343,7 @@ mod tests {
 
     #[test]
     fn ray_is_parallel_to_surface_and_hits() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
@@ -377,7 +377,7 @@ mod tests {
 
     #[test]
     fn ray_is_parallel_to_surface_and_misses() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
diff --git a/crates/fj-core/src/algorithms/intersect/surface_surface.rs b/crates/fj-core/src/algorithms/intersect/surface_surface.rs
index edf2bf724..a5be37894 100644
--- a/crates/fj-core/src/algorithms/intersect/surface_surface.rs
+++ b/crates/fj-core/src/algorithms/intersect/surface_surface.rs
@@ -76,14 +76,14 @@ mod tests {
     use pretty_assertions::assert_eq;
 
     use crate::{
-        geometry::SurfacePath, operations::transform::TransformObject, Instance,
+        geometry::SurfacePath, operations::transform::TransformObject, Core,
     };
 
     use super::SurfaceSurfaceIntersection;
 
     #[test]
     fn plane_plane() {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let xy = core.layers.objects.surfaces.xy_plane();
         let xz = core.layers.objects.surfaces.xz_plane();
diff --git a/crates/fj-core/src/algorithms/triangulate/mod.rs b/crates/fj-core/src/algorithms/triangulate/mod.rs
index 653fe89bc..534cca377 100644
--- a/crates/fj-core/src/algorithms/triangulate/mod.rs
+++ b/crates/fj-core/src/algorithms/triangulate/mod.rs
@@ -84,14 +84,14 @@ mod tests {
             build::{BuildCycle, BuildFace},
             update::{UpdateFace, UpdateRegion},
         },
-        Instance,
+        Core,
     };
 
     use super::Triangulate;
 
     #[test]
     fn simple() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let a = [0., 0.];
         let b = [2., 0.];
@@ -127,7 +127,7 @@ mod tests {
 
     #[test]
     fn simple_hole() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let a = [0., 0.];
         let b = [4., 0.];
@@ -185,7 +185,7 @@ mod tests {
 
     #[test]
     fn sharp_concave_shape() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         //   e       c
         //   |\     /|
diff --git a/crates/fj-core/src/instance.rs b/crates/fj-core/src/core.rs
similarity index 91%
rename from crates/fj-core/src/instance.rs
rename to crates/fj-core/src/core.rs
index 242c2f5d7..ae8c0e39c 100644
--- a/crates/fj-core/src/instance.rs
+++ b/crates/fj-core/src/core.rs
@@ -1,6 +1,6 @@
 //! Main entry point to the `fj-core` API
 //!
-//! See [`Instance`].
+//! See [`Core`].
 
 use crate::{layers::Layers, validate::ValidationConfig};
 
@@ -8,12 +8,12 @@ use crate::{layers::Layers, validate::ValidationConfig};
 ///
 /// This is the main entry point to `fj-core`'s API.
 #[derive(Default)]
-pub struct Instance {
+pub struct Core {
     /// The layers of data that make up the state of a core instance
     pub layers: Layers,
 }
 
-impl Instance {
+impl Core {
     /// Construct an instance of `Instance`
     pub fn new() -> Self {
         Self::default()
diff --git a/crates/fj-core/src/lib.rs b/crates/fj-core/src/lib.rs
index 5f87b5489..6118c0b6d 100644
--- a/crates/fj-core/src/lib.rs
+++ b/crates/fj-core/src/lib.rs
@@ -90,6 +90,6 @@ pub mod queries;
 pub mod storage;
 pub mod validate;
 
-mod instance;
+mod core;
 
-pub use self::instance::Instance;
+pub use self::core::Core;
diff --git a/crates/fj-core/src/operations/build/cycle.rs b/crates/fj-core/src/operations/build/cycle.rs
index 454cf5c20..118c09102 100644
--- a/crates/fj-core/src/operations/build/cycle.rs
+++ b/crates/fj-core/src/operations/build/cycle.rs
@@ -4,7 +4,7 @@ use itertools::Itertools;
 use crate::{
     objects::{Cycle, HalfEdge},
     operations::{build::BuildHalfEdge, insert::Insert, update::UpdateCycle},
-    Instance,
+    Core,
 };
 
 /// Build a [`Cycle`]
@@ -22,14 +22,14 @@ pub trait BuildCycle {
     fn circle(
         center: impl Into<Point<2>>,
         radius: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Cycle {
         let circle = HalfEdge::circle(center, radius, core);
         Cycle::empty().add_half_edges([circle], core)
     }
 
     /// Build a polygon
-    fn polygon<P, Ps>(points: Ps, core: &mut Instance) -> Cycle
+    fn polygon<P, Ps>(points: Ps, core: &mut Core) -> Cycle
     where
         P: Into<Point<2>>,
         Ps: IntoIterator<Item = P>,
diff --git a/crates/fj-core/src/operations/build/face.rs b/crates/fj-core/src/operations/build/face.rs
index 7927e3e48..910a8ce73 100644
--- a/crates/fj-core/src/operations/build/face.rs
+++ b/crates/fj-core/src/operations/build/face.rs
@@ -10,7 +10,7 @@ use crate::{
         insert::{Insert, IsInserted, IsInsertedNo},
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Build a [`Face`]
@@ -20,7 +20,7 @@ use crate::{
 /// [module-level documentation]: super
 pub trait BuildFace {
     /// Build a face with an empty exterior, no interiors, and no color
-    fn unbound(surface: Handle<Surface>, core: &mut Instance) -> Face {
+    fn unbound(surface: Handle<Surface>, core: &mut Core) -> Face {
         let exterior = Cycle::empty().insert(core);
         let region = Region::new(exterior, [], None).insert(core);
         Face::new(surface, region)
@@ -29,7 +29,7 @@ pub trait BuildFace {
     /// Build a triangle
     fn triangle(
         points: [impl Into<Point<3>>; 3],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Polygon<3> {
         let (surface, points_surface) = Surface::plane_from_points(points);
         let surface = surface.insert(core);
@@ -63,7 +63,7 @@ pub trait BuildFace {
     fn polygon<P, Ps>(
         surface: Handle<Surface>,
         points: Ps,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Face
     where
         P: Into<Point<2>>,
diff --git a/crates/fj-core/src/operations/build/half_edge.rs b/crates/fj-core/src/operations/build/half_edge.rs
index 9ccb1e312..b786e7a8e 100644
--- a/crates/fj-core/src/operations/build/half_edge.rs
+++ b/crates/fj-core/src/operations/build/half_edge.rs
@@ -6,7 +6,7 @@ use crate::{
     objects::{Curve, HalfEdge, Vertex},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Build a [`HalfEdge`]
@@ -19,7 +19,7 @@ pub trait BuildHalfEdge {
     fn unjoined(
         path: SurfacePath,
         boundary: impl Into<CurveBoundary<Point<1>>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> HalfEdge {
         let curve = Curve::new().insert(core);
         let start_vertex = Vertex::new().insert(core);
@@ -49,7 +49,7 @@ pub trait BuildHalfEdge {
         start: impl Into<Point<2>>,
         end: impl Into<Point<2>>,
         angle_rad: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> HalfEdge {
         let angle_rad = angle_rad.into();
         if angle_rad <= -Scalar::TAU || angle_rad >= Scalar::TAU {
@@ -70,7 +70,7 @@ pub trait BuildHalfEdge {
     fn circle(
         center: impl Into<Point<2>>,
         radius: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> HalfEdge {
         let path = SurfacePath::circle_from_center_and_radius(center, radius);
         let boundary =
@@ -83,7 +83,7 @@ pub trait BuildHalfEdge {
     fn line_segment(
         points_surface: [impl Into<Point<2>>; 2],
         boundary: Option<[Point<1>; 2]>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> HalfEdge {
         let boundary =
             boundary.unwrap_or_else(|| [[0.], [1.]].map(Point::from));
diff --git a/crates/fj-core/src/operations/build/region.rs b/crates/fj-core/src/operations/build/region.rs
index 01888cb40..cb96c61dc 100644
--- a/crates/fj-core/src/operations/build/region.rs
+++ b/crates/fj-core/src/operations/build/region.rs
@@ -3,7 +3,7 @@ use fj_math::{Point, Scalar};
 use crate::{
     objects::{Cycle, Region},
     operations::{build::BuildCycle, insert::Insert},
-    Instance,
+    Core,
 };
 
 /// Build a [`Region`]
@@ -13,7 +13,7 @@ use crate::{
 /// [module-level documentation]: super
 pub trait BuildRegion {
     /// Build an empty region
-    fn empty(core: &mut Instance) -> Region {
+    fn empty(core: &mut Core) -> Region {
         let exterior = Cycle::empty().insert(core);
         let interiors = [];
         let color = None;
@@ -25,14 +25,14 @@ pub trait BuildRegion {
     fn circle(
         center: impl Into<Point<2>>,
         radius: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Region {
         let exterior = Cycle::circle(center, radius, core).insert(core);
         Region::new(exterior, [], None)
     }
 
     /// Build a polygon
-    fn polygon<P, Ps>(points: Ps, core: &mut Instance) -> Region
+    fn polygon<P, Ps>(points: Ps, core: &mut Core) -> Region
     where
         P: Into<Point<2>>,
         Ps: IntoIterator<Item = P>,
diff --git a/crates/fj-core/src/operations/build/shell.rs b/crates/fj-core/src/operations/build/shell.rs
index 872663ab3..d8860fc82 100644
--- a/crates/fj-core/src/operations/build/shell.rs
+++ b/crates/fj-core/src/operations/build/shell.rs
@@ -15,7 +15,7 @@ use crate::{
             UpdateCycle, UpdateFace, UpdateHalfEdge, UpdateRegion, UpdateShell,
         },
     },
-    Instance,
+    Core,
 };
 
 /// Build a [`Shell`]
@@ -33,7 +33,7 @@ pub trait BuildShell {
     fn from_vertices_and_indices(
         vertices: impl IntoIterator<Item = impl Into<Point<3>>>,
         indices: impl IntoIterator<Item = [usize; 3]>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Shell {
         let vertices = vertices
             .into_iter()
@@ -138,7 +138,7 @@ pub trait BuildShell {
     /// build a correct tetrahedron, regardless of that order.
     fn tetrahedron(
         points: [impl Into<Point<3>>; 4],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> TetrahedronShell {
         let [a, b, c, d] = points.map(Into::into);
 
diff --git a/crates/fj-core/src/operations/build/solid.rs b/crates/fj-core/src/operations/build/solid.rs
index b4e30a894..84a02965e 100644
--- a/crates/fj-core/src/operations/build/solid.rs
+++ b/crates/fj-core/src/operations/build/solid.rs
@@ -7,7 +7,7 @@ use crate::{
         insert::{Insert, IsInsertedYes},
         update::UpdateSolid,
     },
-    Instance,
+    Core,
 };
 
 /// Build a [`Solid`]
@@ -26,7 +26,7 @@ pub trait BuildSolid {
     /// See [`BuildShell::tetrahedron`] for more information.
     fn tetrahedron(
         points: [impl Into<Point<3>>; 4],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Tetrahedron {
         let shell = Shell::tetrahedron(points, core).insert(core);
         let solid = Solid::empty().add_shells([shell.shell.clone()], core);
diff --git a/crates/fj-core/src/operations/holes.rs b/crates/fj-core/src/operations/holes.rs
index 77c0e8f87..350254bb8 100644
--- a/crates/fj-core/src/operations/holes.rs
+++ b/crates/fj-core/src/operations/holes.rs
@@ -5,7 +5,7 @@ use fj_math::{Point, Scalar, Vector};
 use crate::{
     objects::{Cycle, Face, HalfEdge, Region, Shell},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{
@@ -24,7 +24,7 @@ pub trait AddHole {
         location: HoleLocation,
         radius: impl Into<Scalar>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self;
 
     /// Add a through hole between the provided locations
@@ -32,7 +32,7 @@ pub trait AddHole {
         &self,
         locations: [HoleLocation; 2],
         radius: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self;
 }
 
@@ -42,7 +42,7 @@ impl AddHole for Shell {
         location: HoleLocation,
         radius: impl Into<Scalar>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self {
         let entry =
             HalfEdge::circle(location.position, radius, core).insert(core);
@@ -89,7 +89,7 @@ impl AddHole for Shell {
         &self,
         [entry_location, exit_location]: [HoleLocation; 2],
         radius: impl Into<Scalar>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self {
         let radius = radius.into();
 
diff --git a/crates/fj-core/src/operations/insert/insert_trait.rs b/crates/fj-core/src/operations/insert/insert_trait.rs
index 3ec696231..e23cdff6e 100644
--- a/crates/fj-core/src/operations/insert/insert_trait.rs
+++ b/crates/fj-core/src/operations/insert/insert_trait.rs
@@ -5,7 +5,7 @@ use crate::{
     },
     operations::build::{Polygon, TetrahedronShell},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{IsInsertedNo, IsInsertedYes};
@@ -28,7 +28,7 @@ pub trait Insert: Sized {
     /// specific reason to do so, and you are handling validation errors in a
     /// non-standard way.
     #[must_use]
-    fn insert(self, core: &mut Instance) -> Self::Inserted;
+    fn insert(self, core: &mut Core) -> Self::Inserted;
 }
 
 macro_rules! impl_insert {
@@ -37,7 +37,7 @@ macro_rules! impl_insert {
             impl Insert for $ty {
                 type Inserted = Handle<Self>;
 
-                fn insert(self, core: &mut Instance) -> Self::Inserted {
+                fn insert(self, core: &mut Core) -> Self::Inserted {
                     let handle = core.layers.objects.$store.reserve();
                     let object = (handle.clone(), self).into();
                     core.layers.objects.insert(
@@ -73,7 +73,7 @@ where
 {
     type Inserted = Self;
 
-    fn insert(self, _: &mut Instance) -> Self::Inserted {
+    fn insert(self, _: &mut Core) -> Self::Inserted {
         self
     }
 }
@@ -81,7 +81,7 @@ where
 impl<const D: usize> Insert for Polygon<D, IsInsertedNo> {
     type Inserted = Polygon<D, IsInsertedYes>;
 
-    fn insert(self, core: &mut Instance) -> Self::Inserted {
+    fn insert(self, core: &mut Core) -> Self::Inserted {
         Polygon {
             face: self.face.insert(core),
             half_edges: self.half_edges,
@@ -93,7 +93,7 @@ impl<const D: usize> Insert for Polygon<D, IsInsertedNo> {
 impl Insert for TetrahedronShell<IsInsertedNo> {
     type Inserted = TetrahedronShell<IsInsertedYes>;
 
-    fn insert(self, core: &mut Instance) -> Self::Inserted {
+    fn insert(self, core: &mut Core) -> Self::Inserted {
         TetrahedronShell {
             shell: self.shell.insert(core),
             abc: self.abc,
diff --git a/crates/fj-core/src/operations/join/cycle.rs b/crates/fj-core/src/operations/join/cycle.rs
index da78d9beb..e05a8effa 100644
--- a/crates/fj-core/src/operations/join/cycle.rs
+++ b/crates/fj-core/src/operations/join/cycle.rs
@@ -11,14 +11,14 @@ use crate::{
         update::{UpdateCycle, UpdateHalfEdge},
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Join a [`Cycle`] to another
 pub trait JoinCycle {
     /// Add half-edges to the cycle that are joined to the provided ones
     #[must_use]
-    fn add_joined_edges<Es>(&self, edges: Es, core: &mut Instance) -> Self
+    fn add_joined_edges<Es>(&self, edges: Es, core: &mut Core) -> Self
     where
         Es: IntoIterator<
             Item = (Handle<HalfEdge>, SurfacePath, CurveBoundary<Point<1>>),
@@ -72,12 +72,12 @@ pub trait JoinCycle {
         other: &Cycle,
         range: RangeInclusive<usize>,
         other_range: RangeInclusive<usize>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self;
 }
 
 impl JoinCycle for Cycle {
-    fn add_joined_edges<Es>(&self, edges: Es, core: &mut Instance) -> Self
+    fn add_joined_edges<Es>(&self, edges: Es, core: &mut Core) -> Self
     where
         Es: IntoIterator<
             Item = (Handle<HalfEdge>, SurfacePath, CurveBoundary<Point<1>>),
@@ -104,7 +104,7 @@ impl JoinCycle for Cycle {
         other: &Cycle,
         range: RangeInclusive<usize>,
         range_other: RangeInclusive<usize>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self {
         assert_eq!(
             range.end() - range.start(),
diff --git a/crates/fj-core/src/operations/merge.rs b/crates/fj-core/src/operations/merge.rs
index fcf402bd7..560deb63c 100644
--- a/crates/fj-core/src/operations/merge.rs
+++ b/crates/fj-core/src/operations/merge.rs
@@ -3,7 +3,7 @@
 //! See [`Merge`], which is currently the only trait in this module, for more
 //! information.
 
-use crate::{objects::Solid, Instance};
+use crate::{objects::Solid, Core};
 
 use super::update::UpdateSolid;
 
@@ -11,11 +11,11 @@ use super::update::UpdateSolid;
 pub trait Merge {
     /// Merge this solid with another
     #[must_use]
-    fn merge(&self, other: &Self, core: &mut Instance) -> Self;
+    fn merge(&self, other: &Self, core: &mut Core) -> Self;
 }
 
 impl Merge for Solid {
-    fn merge(&self, other: &Self, core: &mut Instance) -> Self {
+    fn merge(&self, other: &Self, core: &mut Core) -> Self {
         self.add_shells(other.shells().iter().cloned(), core)
     }
 }
diff --git a/crates/fj-core/src/operations/replace/curve.rs b/crates/fj-core/src/operations/replace/curve.rs
index 82e9f17ce..9ee37380a 100644
--- a/crates/fj-core/src/operations/replace/curve.rs
+++ b/crates/fj-core/src/operations/replace/curve.rs
@@ -6,7 +6,7 @@ use crate::{
     },
     operations::{insert::Insert, update::UpdateHalfEdge},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::ReplaceOutput;
@@ -23,7 +23,7 @@ pub trait ReplaceCurve: IsObject + Sized {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject>;
 }
 
@@ -32,7 +32,7 @@ impl ReplaceCurve for HalfEdge {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         if original.id() == self.curve().id() {
             ReplaceOutput::Updated(self.update_curve(|_, _| replacement, core))
@@ -47,7 +47,7 @@ impl ReplaceCurve for Cycle {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -76,7 +76,7 @@ impl ReplaceCurve for Region {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -116,7 +116,7 @@ impl ReplaceCurve for Sketch {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -145,7 +145,7 @@ impl ReplaceCurve for Face {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let region = self.region().replace_curve(original, replacement, core);
 
@@ -167,7 +167,7 @@ impl ReplaceCurve for Shell {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -194,7 +194,7 @@ impl ReplaceCurve for Solid {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -223,7 +223,7 @@ impl ReplaceCurve for Handle<HalfEdge> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -236,7 +236,7 @@ impl ReplaceCurve for Handle<Cycle> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -249,7 +249,7 @@ impl ReplaceCurve for Handle<Region> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -262,7 +262,7 @@ impl ReplaceCurve for Handle<Sketch> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -275,7 +275,7 @@ impl ReplaceCurve for Handle<Face> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -288,7 +288,7 @@ impl ReplaceCurve for Handle<Shell> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
@@ -301,7 +301,7 @@ impl ReplaceCurve for Handle<Solid> {
         &self,
         original: &Handle<Curve>,
         replacement: Handle<Curve>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_curve(original, replacement, core)
diff --git a/crates/fj-core/src/operations/replace/half_edge.rs b/crates/fj-core/src/operations/replace/half_edge.rs
index 29d7aa7b5..6ab6ae316 100644
--- a/crates/fj-core/src/operations/replace/half_edge.rs
+++ b/crates/fj-core/src/operations/replace/half_edge.rs
@@ -4,7 +4,7 @@ use crate::{
     objects::{Cycle, Face, HalfEdge, IsObject, Region, Shell, Sketch, Solid},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::ReplaceOutput;
@@ -21,7 +21,7 @@ pub trait ReplaceHalfEdge: IsObject + Sized {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject>;
 }
 
@@ -30,7 +30,7 @@ impl ReplaceHalfEdge for Cycle {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        _: &mut Instance,
+        _: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         if let Some(half_edges) =
             self.half_edges().replace(original, replacements)
@@ -47,7 +47,7 @@ impl ReplaceHalfEdge for Region {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -89,7 +89,7 @@ impl ReplaceHalfEdge for Sketch {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -118,7 +118,7 @@ impl ReplaceHalfEdge for Face {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let region =
             self.region()
@@ -142,7 +142,7 @@ impl ReplaceHalfEdge for Shell {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -170,7 +170,7 @@ impl ReplaceHalfEdge for Solid {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -199,7 +199,7 @@ impl ReplaceHalfEdge for Handle<Cycle> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
@@ -212,7 +212,7 @@ impl ReplaceHalfEdge for Handle<Region> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
@@ -225,7 +225,7 @@ impl ReplaceHalfEdge for Handle<Sketch> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
@@ -238,7 +238,7 @@ impl ReplaceHalfEdge for Handle<Face> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
@@ -251,7 +251,7 @@ impl ReplaceHalfEdge for Handle<Shell> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
@@ -264,7 +264,7 @@ impl ReplaceHalfEdge for Handle<Solid> {
         &self,
         original: &Handle<HalfEdge>,
         replacements: [Handle<HalfEdge>; N],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_half_edge(original, replacements, core)
diff --git a/crates/fj-core/src/operations/replace/vertex.rs b/crates/fj-core/src/operations/replace/vertex.rs
index 6672335a0..968a74372 100644
--- a/crates/fj-core/src/operations/replace/vertex.rs
+++ b/crates/fj-core/src/operations/replace/vertex.rs
@@ -6,7 +6,7 @@ use crate::{
     },
     operations::{insert::Insert, update::UpdateHalfEdge},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::ReplaceOutput;
@@ -23,7 +23,7 @@ pub trait ReplaceVertex: IsObject + Sized {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject>;
 }
 
@@ -32,7 +32,7 @@ impl ReplaceVertex for HalfEdge {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         if original.id() == self.start_vertex().id() {
             ReplaceOutput::Updated(
@@ -49,7 +49,7 @@ impl ReplaceVertex for Cycle {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -78,7 +78,7 @@ impl ReplaceVertex for Region {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -118,7 +118,7 @@ impl ReplaceVertex for Sketch {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -147,7 +147,7 @@ impl ReplaceVertex for Face {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let region = self.region().replace_vertex(original, replacement, core);
 
@@ -169,7 +169,7 @@ impl ReplaceVertex for Shell {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -196,7 +196,7 @@ impl ReplaceVertex for Solid {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -225,7 +225,7 @@ impl ReplaceVertex for Handle<HalfEdge> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
@@ -238,7 +238,7 @@ impl ReplaceVertex for Handle<Cycle> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
@@ -251,7 +251,7 @@ impl ReplaceVertex for Handle<Region> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
@@ -264,7 +264,7 @@ impl ReplaceVertex for Handle<Sketch> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         let mut replacement_happened = false;
 
@@ -293,7 +293,7 @@ impl ReplaceVertex for Handle<Face> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
@@ -306,7 +306,7 @@ impl ReplaceVertex for Handle<Shell> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
@@ -319,7 +319,7 @@ impl ReplaceVertex for Handle<Solid> {
         &self,
         original: &Handle<Vertex>,
         replacement: Handle<Vertex>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> ReplaceOutput<Self, Self::BareObject> {
         self.deref()
             .replace_vertex(original, replacement, core)
diff --git a/crates/fj-core/src/operations/reverse/cycle.rs b/crates/fj-core/src/operations/reverse/cycle.rs
index 3cfc85ddd..7332edc0f 100644
--- a/crates/fj-core/src/operations/reverse/cycle.rs
+++ b/crates/fj-core/src/operations/reverse/cycle.rs
@@ -1,13 +1,13 @@
 use crate::{
     objects::{Cycle, HalfEdge},
     operations::insert::Insert,
-    Instance,
+    Core,
 };
 
 use super::{Reverse, ReverseCurveCoordinateSystems};
 
 impl Reverse for Cycle {
-    fn reverse(&self, core: &mut Instance) -> Self {
+    fn reverse(&self, core: &mut Core) -> Self {
         let mut edges = self
             .half_edges()
             .pairs()
@@ -29,7 +29,7 @@ impl Reverse for Cycle {
 }
 
 impl ReverseCurveCoordinateSystems for Cycle {
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self {
         let edges = self.half_edges().iter().map(|edge| {
             edge.reverse_curve_coordinate_systems(core).insert(core)
         });
diff --git a/crates/fj-core/src/operations/reverse/edge.rs b/crates/fj-core/src/operations/reverse/edge.rs
index 95c1a35c5..e58f7c7b3 100644
--- a/crates/fj-core/src/operations/reverse/edge.rs
+++ b/crates/fj-core/src/operations/reverse/edge.rs
@@ -1,9 +1,9 @@
-use crate::{objects::HalfEdge, Instance};
+use crate::{objects::HalfEdge, Core};
 
 use super::ReverseCurveCoordinateSystems;
 
 impl ReverseCurveCoordinateSystems for HalfEdge {
-    fn reverse_curve_coordinate_systems(&self, _: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, _: &mut Core) -> Self {
         let path = self.path().reverse();
         let boundary = self.boundary().reverse();
 
diff --git a/crates/fj-core/src/operations/reverse/face.rs b/crates/fj-core/src/operations/reverse/face.rs
index 0bcc8cbae..7ec620ebc 100644
--- a/crates/fj-core/src/operations/reverse/face.rs
+++ b/crates/fj-core/src/operations/reverse/face.rs
@@ -6,27 +6,27 @@ use crate::{
         build::Polygon,
         insert::{Insert, IsInsertedNo, IsInsertedYes},
     },
-    Instance,
+    Core,
 };
 
 use super::{Reverse, ReverseCurveCoordinateSystems};
 
 impl Reverse for Face {
-    fn reverse(&self, core: &mut Instance) -> Self {
+    fn reverse(&self, core: &mut Core) -> Self {
         let region = self.region().reverse(core).insert(core);
         Face::new(self.surface().clone(), region)
     }
 }
 
 impl<const D: usize> Reverse for Polygon<D, IsInsertedNo> {
-    fn reverse(&self, core: &mut Instance) -> Self {
+    fn reverse(&self, core: &mut Core) -> Self {
         let face = self.face.borrow().reverse(core);
         self.replace_face(face)
     }
 }
 
 impl<const D: usize> Reverse for Polygon<D, IsInsertedYes> {
-    fn reverse(&self, core: &mut Instance) -> Self {
+    fn reverse(&self, core: &mut Core) -> Self {
         let face: &Face = self.face.borrow();
         let face = face.reverse(core).insert(core);
 
@@ -35,7 +35,7 @@ impl<const D: usize> Reverse for Polygon<D, IsInsertedYes> {
 }
 
 impl ReverseCurveCoordinateSystems for Face {
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self {
         let region = self
             .region()
             .reverse_curve_coordinate_systems(core)
@@ -47,7 +47,7 @@ impl ReverseCurveCoordinateSystems for Face {
 impl<const D: usize> ReverseCurveCoordinateSystems
     for Polygon<D, IsInsertedNo>
 {
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self {
         let face = self.face.borrow().reverse_curve_coordinate_systems(core);
         self.replace_face(face)
     }
@@ -56,7 +56,7 @@ impl<const D: usize> ReverseCurveCoordinateSystems
 impl<const D: usize> ReverseCurveCoordinateSystems
     for Polygon<D, IsInsertedYes>
 {
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self {
         let face: &Face = self.face.borrow();
         let face = face.reverse_curve_coordinate_systems(core).insert(core);
 
diff --git a/crates/fj-core/src/operations/reverse/mod.rs b/crates/fj-core/src/operations/reverse/mod.rs
index 3ebad8284..ae130cec8 100644
--- a/crates/fj-core/src/operations/reverse/mod.rs
+++ b/crates/fj-core/src/operations/reverse/mod.rs
@@ -1,6 +1,6 @@
 //! Reverse the direction/orientation of objects
 
-use crate::Instance;
+use crate::Core;
 
 mod cycle;
 mod edge;
@@ -11,7 +11,7 @@ mod region;
 pub trait Reverse {
     /// Reverse the direction/orientation of the object
     #[must_use]
-    fn reverse(&self, core: &mut Instance) -> Self;
+    fn reverse(&self, core: &mut Core) -> Self;
 }
 
 /// Reverse the direction of the curve coordinate systems within an object
@@ -20,5 +20,5 @@ pub trait ReverseCurveCoordinateSystems {
     ///
     /// This will not have any effect on object positions in global coordinates.
     #[must_use]
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self;
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self;
 }
diff --git a/crates/fj-core/src/operations/reverse/region.rs b/crates/fj-core/src/operations/reverse/region.rs
index 712b387a9..8af95d882 100644
--- a/crates/fj-core/src/operations/reverse/region.rs
+++ b/crates/fj-core/src/operations/reverse/region.rs
@@ -1,9 +1,9 @@
-use crate::{objects::Region, operations::insert::Insert, Instance};
+use crate::{objects::Region, operations::insert::Insert, Core};
 
 use super::{Reverse, ReverseCurveCoordinateSystems};
 
 impl Reverse for Region {
-    fn reverse(&self, core: &mut Instance) -> Self {
+    fn reverse(&self, core: &mut Core) -> Self {
         let exterior = self.exterior().reverse(core).insert(core);
         let interiors = self
             .interiors()
@@ -15,7 +15,7 @@ impl Reverse for Region {
 }
 
 impl ReverseCurveCoordinateSystems for Region {
-    fn reverse_curve_coordinate_systems(&self, core: &mut Instance) -> Self {
+    fn reverse_curve_coordinate_systems(&self, core: &mut Core) -> Self {
         let exterior = self
             .exterior()
             .reverse_curve_coordinate_systems(core)
diff --git a/crates/fj-core/src/operations/split/edge.rs b/crates/fj-core/src/operations/split/edge.rs
index 19b4368d8..f2b378839 100644
--- a/crates/fj-core/src/operations/split/edge.rs
+++ b/crates/fj-core/src/operations/split/edge.rs
@@ -8,7 +8,7 @@ use crate::{
     },
     queries::SiblingOfHalfEdge,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Split a pair of [`HalfEdge`]s into two
@@ -23,7 +23,7 @@ pub trait SplitEdge: Sized {
         &self,
         half_edge: &Handle<HalfEdge>,
         point: impl Into<Point<1>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Self, [[Handle<HalfEdge>; 2]; 2]);
 }
 
@@ -32,7 +32,7 @@ impl SplitEdge for Shell {
         &self,
         half_edge: &Handle<HalfEdge>,
         point: impl Into<Point<1>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Self, [[Handle<HalfEdge>; 2]; 2]) {
         let point = point.into();
 
diff --git a/crates/fj-core/src/operations/split/face.rs b/crates/fj-core/src/operations/split/face.rs
index a7f489e9a..f512e24a6 100644
--- a/crates/fj-core/src/operations/split/face.rs
+++ b/crates/fj-core/src/operations/split/face.rs
@@ -14,7 +14,7 @@ use crate::{
         },
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Split a face into two
@@ -40,7 +40,7 @@ pub trait SplitFace: Sized {
         &self,
         face: &Handle<Face>,
         line: [(&Handle<HalfEdge>, impl Into<Point<1>>); 2],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Self, [Handle<Face>; 2]);
 }
 
@@ -49,7 +49,7 @@ impl SplitFace for Shell {
         &self,
         face: &Handle<Face>,
         line: [(&Handle<HalfEdge>, impl Into<Point<1>>); 2],
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Self, [Handle<Face>; 2]) {
         // The code below might assume that the half-edges that define the line
         // are part of the face's exterior. Let's make that explicit here.
diff --git a/crates/fj-core/src/operations/split/half_edge.rs b/crates/fj-core/src/operations/split/half_edge.rs
index f573dea8a..cb2d0d8e5 100644
--- a/crates/fj-core/src/operations/split/half_edge.rs
+++ b/crates/fj-core/src/operations/split/half_edge.rs
@@ -3,7 +3,7 @@ use fj_math::Point;
 use crate::{
     objects::{HalfEdge, Vertex},
     operations::insert::Insert,
-    Instance,
+    Core,
 };
 
 /// Split a [`HalfEdge`] into two
@@ -27,7 +27,7 @@ pub trait SplitHalfEdge {
     fn split_half_edge(
         &self,
         point: impl Into<Point<1>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> [HalfEdge; 2];
 }
 
@@ -35,7 +35,7 @@ impl SplitHalfEdge for HalfEdge {
     fn split_half_edge(
         &self,
         point: impl Into<Point<1>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> [HalfEdge; 2] {
         let point = point.into();
 
diff --git a/crates/fj-core/src/operations/sweep/cycle.rs b/crates/fj-core/src/operations/sweep/cycle.rs
index 83bfbedb7..6b7c4b092 100644
--- a/crates/fj-core/src/operations/sweep/cycle.rs
+++ b/crates/fj-core/src/operations/sweep/cycle.rs
@@ -6,7 +6,7 @@ use crate::{
     operations::{
         build::BuildCycle, join::JoinCycle, sweep::half_edge::SweepHalfEdge,
     },
-    Instance,
+    Core,
 };
 
 use super::SweepCache;
@@ -41,7 +41,7 @@ pub trait SweepCycle {
         color: Option<Color>,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> SweptCycle;
 }
 
@@ -52,7 +52,7 @@ impl SweepCycle for Cycle {
         color: Option<Color>,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> SweptCycle {
         let path = path.into();
 
diff --git a/crates/fj-core/src/operations/sweep/face.rs b/crates/fj-core/src/operations/sweep/face.rs
index d6086c0d3..439b8b0cd 100644
--- a/crates/fj-core/src/operations/sweep/face.rs
+++ b/crates/fj-core/src/operations/sweep/face.rs
@@ -4,7 +4,7 @@ use crate::{
     objects::{Face, Shell},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{SweepCache, SweepRegion};
@@ -20,7 +20,7 @@ pub trait SweepFace {
         &self,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Shell;
 }
 
@@ -29,7 +29,7 @@ impl SweepFace for Handle<Face> {
         &self,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Shell {
         // Please note that this function uses the words "bottom" and "top" in a
         // specific sense:
diff --git a/crates/fj-core/src/operations/sweep/half_edge.rs b/crates/fj-core/src/operations/sweep/half_edge.rs
index c20e5efea..f88efdd1c 100644
--- a/crates/fj-core/src/operations/sweep/half_edge.rs
+++ b/crates/fj-core/src/operations/sweep/half_edge.rs
@@ -9,7 +9,7 @@ use crate::{
         update::{UpdateCycle, UpdateHalfEdge},
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{vertex::SweepVertex, SweepCache, SweepSurfacePath};
@@ -40,7 +40,7 @@ pub trait SweepHalfEdge {
         color: Option<Color>,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Face, Handle<HalfEdge>);
 }
 
@@ -52,7 +52,7 @@ impl SweepHalfEdge for HalfEdge {
         color: Option<Color>,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Face, Handle<HalfEdge>) {
         let path = path.into();
 
diff --git a/crates/fj-core/src/operations/sweep/region.rs b/crates/fj-core/src/operations/sweep/region.rs
index 39a374705..608e8d097 100644
--- a/crates/fj-core/src/operations/sweep/region.rs
+++ b/crates/fj-core/src/operations/sweep/region.rs
@@ -7,7 +7,7 @@ use crate::{
         insert::Insert, reverse::Reverse, transform::TransformObject,
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{SweepCache, SweepCycle};
@@ -34,7 +34,7 @@ pub trait SweepRegion {
         surface: &Surface,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> SweptRegion;
 }
 
@@ -44,7 +44,7 @@ impl SweepRegion for Region {
         surface: &Surface,
         path: impl Into<Vector<3>>,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> SweptRegion {
         let path = path.into();
 
@@ -99,7 +99,7 @@ fn sweep_cycle(
     faces: &mut Vec<Face>,
     path: Vector<3>,
     cache: &mut SweepCache,
-    core: &mut Instance,
+    core: &mut Core,
 ) -> Handle<Cycle> {
     let swept_cycle = bottom_cycle.reverse(core).sweep_cycle(
         bottom_surface,
diff --git a/crates/fj-core/src/operations/sweep/shell_face.rs b/crates/fj-core/src/operations/sweep/shell_face.rs
index 11af14481..3deb888cd 100644
--- a/crates/fj-core/src/operations/sweep/shell_face.rs
+++ b/crates/fj-core/src/operations/sweep/shell_face.rs
@@ -9,7 +9,7 @@ use crate::{
         update::UpdateShell,
     },
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// # Sweep a [`Face`] that is part of a [`Shell`]
@@ -34,7 +34,7 @@ pub trait SweepFaceOfShell {
         &self,
         face: Handle<Face>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self;
 }
 
@@ -43,7 +43,7 @@ impl SweepFaceOfShell for Shell {
         &self,
         face: Handle<Face>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self {
         let path = path.into();
 
diff --git a/crates/fj-core/src/operations/sweep/sketch.rs b/crates/fj-core/src/operations/sweep/sketch.rs
index 3d5a625d9..5e1a0e141 100644
--- a/crates/fj-core/src/operations/sweep/sketch.rs
+++ b/crates/fj-core/src/operations/sweep/sketch.rs
@@ -5,7 +5,7 @@ use crate::{
     objects::{Face, Sketch, Solid, Surface},
     operations::{insert::Insert, reverse::Reverse},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::{face::SweepFace, SweepCache};
@@ -21,7 +21,7 @@ pub trait SweepSketch {
         &self,
         surface: Handle<Surface>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Solid;
 }
 
@@ -30,7 +30,7 @@ impl SweepSketch for Sketch {
         &self,
         surface: Handle<Surface>,
         path: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Solid {
         let path = path.into();
         let mut cache = SweepCache::default();
diff --git a/crates/fj-core/src/operations/sweep/vertex.rs b/crates/fj-core/src/operations/sweep/vertex.rs
index 129785738..411d760c8 100644
--- a/crates/fj-core/src/operations/sweep/vertex.rs
+++ b/crates/fj-core/src/operations/sweep/vertex.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Curve, Vertex},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 use super::SweepCache;
@@ -34,7 +34,7 @@ pub trait SweepVertex: Sized {
     fn sweep_vertex(
         &self,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Handle<Curve>, Handle<Vertex>);
 }
 
@@ -42,7 +42,7 @@ impl SweepVertex for Handle<Vertex> {
     fn sweep_vertex(
         &self,
         cache: &mut SweepCache,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> (Handle<Curve>, Handle<Vertex>) {
         let curve = cache
             .curves
diff --git a/crates/fj-core/src/operations/transform/curve.rs b/crates/fj-core/src/operations/transform/curve.rs
index 5b17aed34..433ac9b6f 100644
--- a/crates/fj-core/src/operations/transform/curve.rs
+++ b/crates/fj-core/src/operations/transform/curve.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Curve, Instance};
+use crate::{objects::Curve, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Curve {
     fn transform_with_cache(
         &self,
         _: &Transform,
-        _: &mut Instance,
+        _: &mut Core,
         _: &mut TransformCache,
     ) -> Self {
         // There's nothing to actually transform here, as `Curve` holds no data.
diff --git a/crates/fj-core/src/operations/transform/cycle.rs b/crates/fj-core/src/operations/transform/cycle.rs
index 6f64536da..4d2e44ec6 100644
--- a/crates/fj-core/src/operations/transform/cycle.rs
+++ b/crates/fj-core/src/operations/transform/cycle.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Cycle, Instance};
+use crate::{objects::Cycle, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Cycle {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         let edges = self.half_edges().iter().map(|edge| {
diff --git a/crates/fj-core/src/operations/transform/edge.rs b/crates/fj-core/src/operations/transform/edge.rs
index 78781bf1e..5aa5424f1 100644
--- a/crates/fj-core/src/operations/transform/edge.rs
+++ b/crates/fj-core/src/operations/transform/edge.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::HalfEdge, Instance};
+use crate::{objects::HalfEdge, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for HalfEdge {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         // Don't need to transform the path, as that's defined in surface
diff --git a/crates/fj-core/src/operations/transform/face.rs b/crates/fj-core/src/operations/transform/face.rs
index f217a1c18..5ab2bd836 100644
--- a/crates/fj-core/src/operations/transform/face.rs
+++ b/crates/fj-core/src/operations/transform/face.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Face, Instance};
+use crate::{objects::Face, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Face {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         let surface = self
diff --git a/crates/fj-core/src/operations/transform/mod.rs b/crates/fj-core/src/operations/transform/mod.rs
index f3d9edbb2..b47b473f7 100644
--- a/crates/fj-core/src/operations/transform/mod.rs
+++ b/crates/fj-core/src/operations/transform/mod.rs
@@ -18,7 +18,7 @@ use type_map::TypeMap;
 use crate::{
     operations::insert::Insert,
     storage::{Handle, ObjectId},
-    Instance,
+    Core,
 };
 
 /// Transform an object
@@ -32,7 +32,7 @@ use crate::{
 /// hasn't been done so far, is that no one has put in the work yet.
 pub trait TransformObject: Sized {
     /// Transform the object
-    fn transform(&self, transform: &Transform, core: &mut Instance) -> Self {
+    fn transform(&self, transform: &Transform, core: &mut Core) -> Self {
         let mut cache = TransformCache::default();
         self.transform_with_cache(transform, core, &mut cache)
     }
@@ -41,18 +41,14 @@ pub trait TransformObject: Sized {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self;
 
     /// Translate the object
     ///
     /// Convenience wrapper around [`TransformObject::transform`].
-    fn translate(
-        &self,
-        offset: impl Into<Vector<3>>,
-        core: &mut Instance,
-    ) -> Self {
+    fn translate(&self, offset: impl Into<Vector<3>>, core: &mut Core) -> Self {
         self.transform(&Transform::translation(offset), core)
     }
 
@@ -62,7 +58,7 @@ pub trait TransformObject: Sized {
     fn rotate(
         &self,
         axis_angle: impl Into<Vector<3>>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self {
         self.transform(&Transform::rotation(axis_angle), core)
     }
@@ -75,7 +71,7 @@ where
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         if let Some(object) = cache.get(self) {
diff --git a/crates/fj-core/src/operations/transform/region.rs b/crates/fj-core/src/operations/transform/region.rs
index 48e79e2bf..f1fb393e7 100644
--- a/crates/fj-core/src/operations/transform/region.rs
+++ b/crates/fj-core/src/operations/transform/region.rs
@@ -1,4 +1,4 @@
-use crate::{objects::Region, Instance};
+use crate::{objects::Region, Core};
 
 use super::TransformObject;
 
@@ -6,7 +6,7 @@ impl TransformObject for Region {
     fn transform_with_cache(
         &self,
         transform: &fj_math::Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut super::TransformCache,
     ) -> Self {
         // Color does not need to be transformed.
diff --git a/crates/fj-core/src/operations/transform/shell.rs b/crates/fj-core/src/operations/transform/shell.rs
index 4132b6af1..7b8feaf2e 100644
--- a/crates/fj-core/src/operations/transform/shell.rs
+++ b/crates/fj-core/src/operations/transform/shell.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Shell, Instance};
+use crate::{objects::Shell, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Shell {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         let faces = self
diff --git a/crates/fj-core/src/operations/transform/solid.rs b/crates/fj-core/src/operations/transform/solid.rs
index a1c3ddb66..22253d571 100644
--- a/crates/fj-core/src/operations/transform/solid.rs
+++ b/crates/fj-core/src/operations/transform/solid.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Solid, Instance};
+use crate::{objects::Solid, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Solid {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        core: &mut Instance,
+        core: &mut Core,
         cache: &mut TransformCache,
     ) -> Self {
         let shells =
diff --git a/crates/fj-core/src/operations/transform/surface.rs b/crates/fj-core/src/operations/transform/surface.rs
index eb21e06d0..579d606b4 100644
--- a/crates/fj-core/src/operations/transform/surface.rs
+++ b/crates/fj-core/src/operations/transform/surface.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Surface, Instance};
+use crate::{objects::Surface, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Surface {
     fn transform_with_cache(
         &self,
         transform: &Transform,
-        _: &mut Instance,
+        _: &mut Core,
         _: &mut TransformCache,
     ) -> Self {
         let geometry = self.geometry().transform(transform);
diff --git a/crates/fj-core/src/operations/transform/vertex.rs b/crates/fj-core/src/operations/transform/vertex.rs
index c89bbe38a..a08ef57dc 100644
--- a/crates/fj-core/src/operations/transform/vertex.rs
+++ b/crates/fj-core/src/operations/transform/vertex.rs
@@ -1,6 +1,6 @@
 use fj_math::Transform;
 
-use crate::{objects::Vertex, Instance};
+use crate::{objects::Vertex, Core};
 
 use super::{TransformCache, TransformObject};
 
@@ -8,7 +8,7 @@ impl TransformObject for Vertex {
     fn transform_with_cache(
         &self,
         _: &Transform,
-        _: &mut Instance,
+        _: &mut Core,
         _: &mut TransformCache,
     ) -> Self {
         // There's nothing to actually transform here, as `Vertex` holds no
diff --git a/crates/fj-core/src/operations/update/cycle.rs b/crates/fj-core/src/operations/update/cycle.rs
index a94ea5090..3a56af1e0 100644
--- a/crates/fj-core/src/operations/update/cycle.rs
+++ b/crates/fj-core/src/operations/update/cycle.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Cycle, HalfEdge},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Cycle`]
@@ -12,7 +12,7 @@ pub trait UpdateCycle {
     fn add_half_edges<T>(
         &self,
         half_edges: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<HalfEdge>>;
@@ -28,8 +28,8 @@ pub trait UpdateCycle {
     fn update_half_edge<T, const N: usize>(
         &self,
         handle: &Handle<HalfEdge>,
-        update: impl FnOnce(&Handle<HalfEdge>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<HalfEdge>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<HalfEdge>>;
@@ -39,7 +39,7 @@ impl UpdateCycle for Cycle {
     fn add_half_edges<T>(
         &self,
         half_edges: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<HalfEdge>>,
@@ -54,8 +54,8 @@ impl UpdateCycle for Cycle {
     fn update_half_edge<T, const N: usize>(
         &self,
         handle: &Handle<HalfEdge>,
-        update: impl FnOnce(&Handle<HalfEdge>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<HalfEdge>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<HalfEdge>>,
diff --git a/crates/fj-core/src/operations/update/face.rs b/crates/fj-core/src/operations/update/face.rs
index ac9d91484..8df9dc624 100644
--- a/crates/fj-core/src/operations/update/face.rs
+++ b/crates/fj-core/src/operations/update/face.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Face, Region},
     operations::{build::Polygon, insert::Insert},
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Face`]
@@ -11,8 +11,8 @@ pub trait UpdateFace {
     #[must_use]
     fn update_region<T>(
         &self,
-        update: impl FnOnce(&Handle<Region>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Region>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>;
@@ -21,8 +21,8 @@ pub trait UpdateFace {
 impl UpdateFace for Face {
     fn update_region<T>(
         &self,
-        update: impl FnOnce(&Handle<Region>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Region>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>,
@@ -35,8 +35,8 @@ impl UpdateFace for Face {
 impl<const D: usize> UpdateFace for Polygon<D> {
     fn update_region<T>(
         &self,
-        update: impl FnOnce(&Handle<Region>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Region>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>,
diff --git a/crates/fj-core/src/operations/update/half_edge.rs b/crates/fj-core/src/operations/update/half_edge.rs
index dfd96f579..e04acbb6c 100644
--- a/crates/fj-core/src/operations/update/half_edge.rs
+++ b/crates/fj-core/src/operations/update/half_edge.rs
@@ -5,7 +5,7 @@ use crate::{
     objects::{Curve, HalfEdge, Vertex},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`HalfEdge`]
@@ -28,8 +28,8 @@ pub trait UpdateHalfEdge {
     #[must_use]
     fn update_curve<T>(
         &self,
-        update: impl FnOnce(&Handle<Curve>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Curve>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Curve>>;
@@ -38,8 +38,8 @@ pub trait UpdateHalfEdge {
     #[must_use]
     fn update_start_vertex<T>(
         &self,
-        update: impl FnOnce(&Handle<Vertex>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Vertex>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Vertex>>;
@@ -72,8 +72,8 @@ impl UpdateHalfEdge for HalfEdge {
 
     fn update_curve<T>(
         &self,
-        update: impl FnOnce(&Handle<Curve>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Curve>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Curve>>,
@@ -88,8 +88,8 @@ impl UpdateHalfEdge for HalfEdge {
 
     fn update_start_vertex<T>(
         &self,
-        update: impl FnOnce(&Handle<Vertex>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Vertex>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Vertex>>,
diff --git a/crates/fj-core/src/operations/update/region.rs b/crates/fj-core/src/operations/update/region.rs
index f3a6338e3..adff50ef1 100644
--- a/crates/fj-core/src/operations/update/region.rs
+++ b/crates/fj-core/src/operations/update/region.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Cycle, Region},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Region`]
@@ -11,8 +11,8 @@ pub trait UpdateRegion {
     #[must_use]
     fn update_exterior<T>(
         &self,
-        update: impl FnOnce(&Handle<Cycle>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Cycle>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>;
@@ -22,7 +22,7 @@ pub trait UpdateRegion {
     fn add_interiors<T>(
         &self,
         interiors: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>;
@@ -38,8 +38,8 @@ pub trait UpdateRegion {
     fn update_interior<T, const N: usize>(
         &self,
         handle: &Handle<Cycle>,
-        update: impl FnOnce(&Handle<Cycle>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Cycle>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>;
@@ -48,8 +48,8 @@ pub trait UpdateRegion {
 impl UpdateRegion for Region {
     fn update_exterior<T>(
         &self,
-        update: impl FnOnce(&Handle<Cycle>, &mut Instance) -> T,
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Cycle>, &mut Core) -> T,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>,
@@ -61,7 +61,7 @@ impl UpdateRegion for Region {
     fn add_interiors<T>(
         &self,
         interiors: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>,
@@ -74,8 +74,8 @@ impl UpdateRegion for Region {
     fn update_interior<T, const N: usize>(
         &self,
         handle: &Handle<Cycle>,
-        update: impl FnOnce(&Handle<Cycle>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Cycle>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Cycle>>,
diff --git a/crates/fj-core/src/operations/update/shell.rs b/crates/fj-core/src/operations/update/shell.rs
index 0c83c2240..5116b89dd 100644
--- a/crates/fj-core/src/operations/update/shell.rs
+++ b/crates/fj-core/src/operations/update/shell.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Face, Shell},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Shell`]
@@ -12,7 +12,7 @@ pub trait UpdateShell {
     fn add_faces<T>(
         &self,
         faces: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Face>>;
@@ -28,8 +28,8 @@ pub trait UpdateShell {
     fn update_face<T, const N: usize>(
         &self,
         handle: &Handle<Face>,
-        update: impl FnOnce(&Handle<Face>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Face>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Face>>;
@@ -43,7 +43,7 @@ impl UpdateShell for Shell {
     fn add_faces<T>(
         &self,
         faces: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Face>>,
@@ -56,8 +56,8 @@ impl UpdateShell for Shell {
     fn update_face<T, const N: usize>(
         &self,
         handle: &Handle<Face>,
-        update: impl FnOnce(&Handle<Face>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Face>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Face>>,
diff --git a/crates/fj-core/src/operations/update/sketch.rs b/crates/fj-core/src/operations/update/sketch.rs
index a6d568eb6..e13087e44 100644
--- a/crates/fj-core/src/operations/update/sketch.rs
+++ b/crates/fj-core/src/operations/update/sketch.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Region, Sketch},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Sketch`]
@@ -12,7 +12,7 @@ pub trait UpdateSketch {
     fn add_regions<T>(
         &self,
         regions: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>;
@@ -28,8 +28,8 @@ pub trait UpdateSketch {
     fn update_region<T, const N: usize>(
         &self,
         handle: &Handle<Region>,
-        update: impl FnOnce(&Handle<Region>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Region>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>;
@@ -39,7 +39,7 @@ impl UpdateSketch for Sketch {
     fn add_regions<T>(
         &self,
         regions: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>,
@@ -52,8 +52,8 @@ impl UpdateSketch for Sketch {
     fn update_region<T, const N: usize>(
         &self,
         handle: &Handle<Region>,
-        update: impl FnOnce(&Handle<Region>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Region>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Region>>,
diff --git a/crates/fj-core/src/operations/update/solid.rs b/crates/fj-core/src/operations/update/solid.rs
index 180f9ac87..c6ce788bc 100644
--- a/crates/fj-core/src/operations/update/solid.rs
+++ b/crates/fj-core/src/operations/update/solid.rs
@@ -2,7 +2,7 @@ use crate::{
     objects::{Shell, Solid},
     operations::insert::Insert,
     storage::Handle,
-    Instance,
+    Core,
 };
 
 /// Update a [`Solid`]
@@ -12,7 +12,7 @@ pub trait UpdateSolid {
     fn add_shells<T>(
         &self,
         shells: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Shell>>;
@@ -28,8 +28,8 @@ pub trait UpdateSolid {
     fn update_shell<T, const N: usize>(
         &self,
         handle: &Handle<Shell>,
-        update: impl FnOnce(&Handle<Shell>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Shell>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Shell>>;
@@ -39,7 +39,7 @@ impl UpdateSolid for Solid {
     fn add_shells<T>(
         &self,
         shells: impl IntoIterator<Item = T>,
-        core: &mut Instance,
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Shell>>,
@@ -52,8 +52,8 @@ impl UpdateSolid for Solid {
     fn update_shell<T, const N: usize>(
         &self,
         handle: &Handle<Shell>,
-        update: impl FnOnce(&Handle<Shell>, &mut Instance) -> [T; N],
-        core: &mut Instance,
+        update: impl FnOnce(&Handle<Shell>, &mut Core) -> [T; N],
+        core: &mut Core,
     ) -> Self
     where
         T: Insert<Inserted = Handle<Shell>>,
diff --git a/crates/fj-core/src/validate/cycle.rs b/crates/fj-core/src/validate/cycle.rs
index 9bb0f59e8..ce2473e45 100644
--- a/crates/fj-core/src/validate/cycle.rs
+++ b/crates/fj-core/src/validate/cycle.rs
@@ -84,12 +84,12 @@ mod tests {
             update::UpdateCycle,
         },
         validate::{cycle::CycleValidationError, Validate, ValidationError},
-        Instance,
+        Core,
     };
 
     #[test]
     fn edges_connected() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid =
             Cycle::polygon([[0.0, 0.0], [1.0, 0.0], [1.0, 1.0]], &mut core);
diff --git a/crates/fj-core/src/validate/edge.rs b/crates/fj-core/src/validate/edge.rs
index 0eca08d3b..c3e7999d5 100644
--- a/crates/fj-core/src/validate/edge.rs
+++ b/crates/fj-core/src/validate/edge.rs
@@ -71,12 +71,12 @@ mod tests {
         objects::HalfEdge,
         operations::build::BuildHalfEdge,
         validate::{EdgeValidationError, Validate, ValidationError},
-        Instance,
+        Core,
     };
 
     #[test]
     fn edge_vertices_are_coincident() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid =
             HalfEdge::line_segment([[0., 0.], [1., 0.]], None, &mut core);
diff --git a/crates/fj-core/src/validate/face.rs b/crates/fj-core/src/validate/face.rs
index 180c02d5b..fcf16ee14 100644
--- a/crates/fj-core/src/validate/face.rs
+++ b/crates/fj-core/src/validate/face.rs
@@ -94,12 +94,12 @@ mod tests {
             update::{UpdateCycle, UpdateFace, UpdateRegion},
         },
         validate::{FaceValidationError, Validate, ValidationError},
-        Instance,
+        Core,
     };
 
     #[test]
     fn boundary() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let invalid =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core);
@@ -129,7 +129,7 @@ mod tests {
 
     #[test]
     fn interior_winding() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid =
             Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
diff --git a/crates/fj-core/src/validate/shell.rs b/crates/fj-core/src/validate/shell.rs
index c75e8546e..5dba7492c 100644
--- a/crates/fj-core/src/validate/shell.rs
+++ b/crates/fj-core/src/validate/shell.rs
@@ -404,12 +404,12 @@ mod tests {
             },
         },
         validate::{shell::ShellValidationError, Validate, ValidationError},
-        Instance,
+        Core,
     };
 
     #[test]
     fn curve_coordinate_system_mismatch() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid = Shell::tetrahedron(
             [[0., 0., 0.], [0., 1., 0.], [1., 0., 0.], [0., 0., 1.]],
@@ -456,7 +456,7 @@ mod tests {
 
     #[test]
     fn half_edge_has_no_sibling() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid = Shell::tetrahedron(
             [[0., 0., 0.], [0., 1., 0.], [1., 0., 0.], [0., 0., 1.]],
@@ -477,7 +477,7 @@ mod tests {
 
     #[test]
     fn coincident_half_edges_are_not_siblings() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let valid = Shell::tetrahedron(
             [[0., 0., 0.], [0., 1., 0.], [1., 0., 0.], [0., 0., 1.]],
diff --git a/crates/fj-core/src/validate/sketch.rs b/crates/fj-core/src/validate/sketch.rs
index d886cd8e3..7de935d23 100644
--- a/crates/fj-core/src/validate/sketch.rs
+++ b/crates/fj-core/src/validate/sketch.rs
@@ -59,12 +59,12 @@ mod tests {
             references::ReferenceCountError, SketchValidationError, Validate,
             ValidationError,
         },
-        Instance,
+        Core,
     };
 
     #[test]
     fn should_find_cycle_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let shared_cycle = Cycle::new(vec![]).insert(&mut core);
 
@@ -97,7 +97,7 @@ mod tests {
 
     #[test]
     fn should_find_half_edge_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let half_edge =
             HalfEdge::line_segment([[0., 0.], [1., 0.]], None, &mut core)
diff --git a/crates/fj-core/src/validate/solid.rs b/crates/fj-core/src/validate/solid.rs
index cc705419d..befa649eb 100644
--- a/crates/fj-core/src/validate/solid.rs
+++ b/crates/fj-core/src/validate/solid.rs
@@ -185,12 +185,12 @@ mod tests {
             references::ReferenceCountError, SolidValidationError, Validate,
             ValidationError,
         },
-        Instance,
+        Core,
     };
 
     #[test]
     fn should_find_face_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let shared_face = Face::new(
             Surface::new(SurfaceGeometry {
@@ -243,7 +243,7 @@ mod tests {
 
     #[test]
     fn should_find_region_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let shared_region = Region::new(
             Cycle::new(vec![
@@ -296,7 +296,7 @@ mod tests {
 
     #[test]
     fn should_find_cycle_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let shared_cycle =
             Cycle::new(vec![
@@ -346,7 +346,7 @@ mod tests {
 
     #[test]
     fn should_find_half_edge_multiple_references() -> anyhow::Result<()> {
-        let mut core = Instance::new();
+        let mut core = Core::new();
 
         let shared_edge =
             HalfEdge::circle([0., 0.], 1., &mut core).insert(&mut core);
diff --git a/crates/fj/src/instance.rs b/crates/fj/src/instance.rs
index 6a07f2256..28e575d64 100644
--- a/crates/fj/src/instance.rs
+++ b/crates/fj/src/instance.rs
@@ -7,6 +7,7 @@ use fj_core::{
         triangulate::Triangulate,
     },
     validate::{ValidationConfig, ValidationErrors},
+    Core,
 };
 use fj_interop::Model;
 use fj_math::{Aabb, Point, Scalar};
@@ -20,7 +21,7 @@ use crate::Args;
 #[derive(Default)]
 pub struct Instance {
     /// The instance of the Fornjot core
-    pub core: fj_core::Instance,
+    pub core: Core,
 }
 
 impl Instance {
@@ -31,7 +32,7 @@ impl Instance {
 
     /// Construct an instance of `Instance`, using the provided configuration
     pub fn with_validation_config(config: ValidationConfig) -> Self {
-        let core = fj_core::Instance::with_validation_config(config);
+        let core = fj_core::Core::with_validation_config(config);
         Self { core }
     }
 
diff --git a/models/all/src/lib.rs b/models/all/src/lib.rs
index d0520cd32..7e71b4c97 100644
--- a/models/all/src/lib.rs
+++ b/models/all/src/lib.rs
@@ -8,7 +8,7 @@ use fj::{
     math::{Scalar, Vector},
 };
 
-pub fn model(core: &mut fj::core::Instance) -> Solid {
+pub fn model(core: &mut fj::core::Core) -> Solid {
     // Just combine all the other models using offsets/rotations that won't
     // result in neat vertex positions or axis-aligned edges/faces. This is
     // useful for testing.
diff --git a/models/color/src/lib.rs b/models/color/src/lib.rs
index fab80c971..0e32e7186 100644
--- a/models/color/src/lib.rs
+++ b/models/color/src/lib.rs
@@ -7,7 +7,7 @@ use fj::core::{
     },
 };
 
-pub fn model(core: &mut fj::core::Instance) -> Solid {
+pub fn model(core: &mut fj::core::Core) -> Solid {
     let size = 1.;
     let cuboid = cuboid::model([size, size, size], core);
 
diff --git a/models/cuboid/src/lib.rs b/models/cuboid/src/lib.rs
index 047d04dd1..38a0da818 100644
--- a/models/cuboid/src/lib.rs
+++ b/models/cuboid/src/lib.rs
@@ -10,10 +10,7 @@ use fj::{
     math::{Scalar, Vector},
 };
 
-pub fn model(
-    size: impl Into<Vector<3>>,
-    core: &mut fj::core::Instance,
-) -> Solid {
+pub fn model(size: impl Into<Vector<3>>, core: &mut fj::core::Core) -> Solid {
     let [x, y, z] = size.into().components;
 
     let bottom_surface = core.layers.objects.surfaces.xy_plane();
diff --git a/models/holes/src/lib.rs b/models/holes/src/lib.rs
index 42da64881..527d44525 100644
--- a/models/holes/src/lib.rs
+++ b/models/holes/src/lib.rs
@@ -9,10 +9,7 @@ use fj::{
     math::Scalar,
 };
 
-pub fn model(
-    radius: impl Into<Scalar>,
-    core: &mut fj::core::Instance,
-) -> Solid {
+pub fn model(radius: impl Into<Scalar>, core: &mut fj::core::Core) -> Solid {
     let radius = radius.into();
 
     let size = radius * 4.;
diff --git a/models/spacer/src/lib.rs b/models/spacer/src/lib.rs
index 2a58de130..d51cc0e8b 100644
--- a/models/spacer/src/lib.rs
+++ b/models/spacer/src/lib.rs
@@ -15,7 +15,7 @@ pub fn model(
     outer: f64,
     inner: f64,
     height: f64,
-    core: &mut fj::core::Instance,
+    core: &mut fj::core::Core,
 ) -> Solid {
     let bottom_surface = core.layers.objects.surfaces.xy_plane();
     let sweep_path = Vector::from([0., 0., height]);
diff --git a/models/split/src/lib.rs b/models/split/src/lib.rs
index 55d90f97e..4d1ca96b3 100644
--- a/models/split/src/lib.rs
+++ b/models/split/src/lib.rs
@@ -5,11 +5,7 @@ use fj::core::{
     },
 };
 
-pub fn model(
-    size: f64,
-    split_pos: f64,
-    core: &mut fj::core::Instance,
-) -> Solid {
+pub fn model(size: f64, split_pos: f64, core: &mut fj::core::Core) -> Solid {
     let cuboid = cuboid::model([size, size, size], core);
 
     cuboid.update_shell(
diff --git a/models/star/src/lib.rs b/models/star/src/lib.rs
index 295d03e16..a3a21cdf3 100644
--- a/models/star/src/lib.rs
+++ b/models/star/src/lib.rs
@@ -18,7 +18,7 @@ pub fn model(
     r1: f64,
     r2: f64,
     h: f64,
-    core: &mut fj::core::Instance,
+    core: &mut fj::core::Core,
 ) -> Solid {
     let num_vertices = num_points * 2;
     let vertex_iter = (0..num_vertices).map(|i| {
diff --git a/models/vertices-indices/src/lib.rs b/models/vertices-indices/src/lib.rs
index 638debb33..0f45596ec 100644
--- a/models/vertices-indices/src/lib.rs
+++ b/models/vertices-indices/src/lib.rs
@@ -6,7 +6,7 @@ use fj::core::{
     },
 };
 
-pub fn model(core: &mut fj::core::Instance) -> Solid {
+pub fn model(core: &mut fj::core::Core) -> Solid {
     Solid::empty().add_shells(
         [Shell::from_vertices_and_indices(
             [[0., 0., 0.], [1., 0., 0.], [0., 1., 0.], [0., 0., 1.]],