diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 70e26b5..fe0695d 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -1,6 +1,8 @@
 name: CI
 
 on:
+  create:
+    tags:
   push:
     branches:
       - main
@@ -32,11 +34,15 @@ jobs:
             coverage: true
     steps:
       - uses: actions/checkout@v4
+
+#     - name: "Set up Julia"
       - uses: julia-actions/setup-julia@latest
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: actions/cache@v4
+
+      - name: Cache artifacts
+        uses: actions/cache@v4
         env:
           cache-name: cache-artifacts
         with:
@@ -46,14 +52,21 @@ jobs:
             ${{ runner.os }}-test-${{ env.cache-name }}-
             ${{ runner.os }}-test-
             ${{ runner.os }}-
-      - uses: julia-actions/julia-buildpkg@v1
-      - uses: julia-actions/julia-runtest@v1
+
+#     - name: "Unit Test"
+      - uses: julia-actions/julia-buildpkg@latest
+      - uses: julia-actions/julia-runtest@latest
+
+#     - name: "Cover"
       - uses: julia-actions/julia-processcoverage@v1
         if: matrix.coverage
       - uses: codecov/codecov-action@v4
         if: matrix.coverage
         with:
           file: lcov.info
+          fail_ci_if_error: false
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       - uses: coverallsapp/github-action@master
         if: matrix.coverage
         with:
diff --git a/Project.toml b/Project.toml
index 57571fa..b9fb1ea 100644
--- a/Project.toml
+++ b/Project.toml
@@ -7,5 +7,6 @@ LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Polynomials = "f27b6e38-b328-58d1-80ce-0feddd5e7a45"
 
 [compat]
+LinearAlgebra = "1"
 Polynomials = "1, 2, 3, 4"
 julia = "1.6"
diff --git a/src/cauchy.jl b/src/cauchy.jl
index 9137244..8dcdea6 100644
--- a/src/cauchy.jl
+++ b/src/cauchy.jl
@@ -54,9 +54,9 @@ struct Cauchy{T,X,Y} <: AbstractMatrix{T}
     y::Y
 
     function Cauchy(
-        x::Union{NTuple{N,<:Tx}, AbstractArray{Tx}},
-        y::Union{NTuple{M,<:Ty}, AbstractArray{Ty}},
-    ) where {N, M, Tx <: Number, Ty <: Number}
+        x::Union{NTuple{N,<:Tx} where {N}, AbstractArray{Tx}},
+        y::Union{NTuple{M,<:Ty} where {M}, AbstractArray{Ty}},
+    ) where {Tx <: Number, Ty <: Number}
         Base.require_one_based_indexing(x)
         Base.require_one_based_indexing(y)
         _cauchy_check(x, y)
diff --git a/src/companion.jl b/src/companion.jl
index 7fed341..1888022 100644
--- a/src/companion.jl
+++ b/src/companion.jl
@@ -85,7 +85,7 @@ function mul!(y::Vector, C::Companion, x::AbstractVector)
     return y
 end
 
-# A <= B * C
+# A ⟸ B * C
 function mul!(A::Matrix, B::AbstractMatrix, C::Companion)
     @boundscheck (size(A) == (size(B,1), size(C,2)) && size(B, 2) == size(C,1)) ||
         throw(DimensionMismatch("mul! arguments incompatible sizes"))
@@ -93,7 +93,7 @@ function mul!(A::Matrix, B::AbstractMatrix, C::Companion)
     @views for j in 1:size(A,2)-1
         @inbounds A[:,j] = B[:,j+1]
     end
-    @inbounds mul!((@view A[:,end]), B, C.c, -1, 0) # A[:,end] <= - B * c
+    @inbounds mul!((@view A[:,end]), B, C.c, -1, 0) # A[:,end] ⟸ - B * c
     return A
 end
 
diff --git a/src/frobenius.jl b/src/frobenius.jl
index e3629fb..f397c12 100644
--- a/src/frobenius.jl
+++ b/src/frobenius.jl
@@ -100,7 +100,7 @@ end
 
 # Linear algebra
 
-# 3-argument mul! mutates first argument: y <= F * x
+# 3-argument mul! mutates first argument: y ⟸ F * x
 # *(F, x) = F * x derives from this automatically in Base
 function mul!(y::Vector, F::Frobenius, x::AbstractVector)
     Base.require_one_based_indexing(x)
diff --git a/test/Project.toml b/test/Project.toml
index adbac9d..205ca81 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,4 +1,5 @@
 [deps]
+Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 Polynomials = "f27b6e38-b328-58d1-80ce-0feddd5e7a45"
diff --git a/test/aqua.jl b/test/aqua.jl
new file mode 100644
index 0000000..06548ad
--- /dev/null
+++ b/test/aqua.jl
@@ -0,0 +1,19 @@
+using SpecialMatrices: SpecialMatrices
+import Aqua
+using Test: @testset
+
+@testset "aqua" begin
+  if VERSION < v"1.11"
+    Aqua.test_all(SpecialMatrices; ambiguities = false)
+  else
+    Aqua.test_all(SpecialMatrices)
+  end
+end
+
+#=
+todo: 1 ambiguity in julia v1.10
+mul!(A::Matrix, B::AbstractMatrix, C::SpecialMatrices.Companion)
+ SpecialMatrices/src/companion.jl:89
+mul!(C::AbstractMatrix, A::LinearAlgebra.AbstractTriangular, B::AbstractMatrix)
+ LinearAlgebra/src/triangular.jl:691
+=#
diff --git a/test/cauchy.jl b/test/cauchy.jl
index a7cd38c..e9a6d01 100644
--- a/test/cauchy.jl
+++ b/test/cauchy.jl
@@ -1,3 +1,8 @@
+# test/cauchy.jl
+
+using SpecialMatrices: Cauchy
+using Test: @test, @test_throws, @inferred
+
 C = @inferred Cauchy(3)
 @test 1 ./ C ≈ [2 3 4; 3 4 5; 4 5 6]
 @test size(C) == (3,3)
diff --git a/test/companion.jl b/test/companion.jl
index c6c6f1a..ee758a3 100644
--- a/test/companion.jl
+++ b/test/companion.jl
@@ -1,5 +1,8 @@
 # test/companion.jl
 
+using SpecialMatrices: Companion
+using Test: @test, @test_throws, @inferred
+
 import LinearAlgebra: mul!
 using OffsetArrays: OffsetArray
 import OffsetArrays # for no_offset_view
diff --git a/test/frobenius.jl b/test/frobenius.jl
index 29bb6b2..fb73aa1 100644
--- a/test/frobenius.jl
+++ b/test/frobenius.jl
@@ -1,3 +1,7 @@
+# test/frobenius.jl
+
+using SpecialMatrices: Frobenius
+using Test: @test, @test_throws, @inferred
 using LinearAlgebra: I
 import LinearAlgebra: mul!
 
diff --git a/test/hilbert.jl b/test/hilbert.jl
index ae82ddc..4533a9a 100644
--- a/test/hilbert.jl
+++ b/test/hilbert.jl
@@ -1,5 +1,9 @@
 # test/hilbert.jl
 
+using SpecialMatrices: Hilbert, InverseHilbert
+using LinearAlgebra: I, det, ishermitian, isposdef
+using Test: @test, @test_throws, @inferred
+
 n = 10
 H = @inferred Hilbert(n)
 @test H isa Hilbert
diff --git a/test/kahan.jl b/test/kahan.jl
index 97f2e07..2e42bd5 100644
--- a/test/kahan.jl
+++ b/test/kahan.jl
@@ -1,5 +1,8 @@
 # test/kahan.jl
 
+using SpecialMatrices: Kahan
+using Test: @test, @inferred
+
 m, n = 3, 5
 A = Kahan(m, n, 0.5, 1e-3)
 
diff --git a/test/runtests.jl b/test/runtests.jl
index 107aa69..ab68cc8 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,6 +1,7 @@
-using SpecialMatrices
-using Test
-using LinearAlgebra
+using SpecialMatrices: SpecialMatrices
+using Test: @test, @test_broken, @testset, detect_ambiguities
+
+include("aqua.jl")
 
 const files = (
     "cauchy",
@@ -18,3 +19,11 @@ const files = (
         include("$f.jl")
     end
 end
+
+@testset "ambiguities" begin
+if VERSION < v"1.11"
+    @test_broken isempty(detect_ambiguities(SpecialMatrices)) # see aqua.jl
+else
+    @test isempty(detect_ambiguities(SpecialMatrices))
+end
+end