diff --git a/README.md b/README.md
index ed771c6..c547383 100644
--- a/README.md
+++ b/README.md
@@ -286,8 +286,8 @@ Please see the internal `defaultComparer` for an example, bearing in mind that i
 
 ## Set
 
-The `Set` represents a collection of unique values. It uses a `map[T]struct{}`, so it carries over some characteristics from the built-in Go `map` type.
-Values neeed to be `comparable`.
+The `Set` represents a collection of unique values, and it is implemented as a
+wrapper around a `Map[T, struct{}]`.
 
 Like Maps, Sets require a `Hasher` to hash keys and check for equality. There are built-in
 hasher implementations for most primitive types such as `int`, `uint`, and
diff --git a/immutable.go b/immutable.go
index b3d7dcb..666bb49 100644
--- a/immutable.go
+++ b/immutable.go
@@ -117,12 +117,8 @@ func (l *List[T]) set(index int, value T, mutable bool) *List[T] {
 }
 
 // Append returns a new list with value added to the end of the list.
-func (l *List[T]) Append(values ...T) *List[T] {
-	other := l.clone()
-	for _, value := range values {
-		other.append(value, true)
-	}
-	return other
+func (l *List[T]) Append(value T) *List[T] {
+	return l.append(value, false)
 }
 
 func (l *List[T]) append(value T, mutable bool) *List[T] {
@@ -145,12 +141,8 @@ func (l *List[T]) append(value T, mutable bool) *List[T] {
 }
 
 // Prepend returns a new list with value(s) added to the beginning of the list.
-func (l *List[T]) Prepend(values ...T) *List[T] {
-	other := l.clone()
-	for i := len(values) - 1; i >= 0; i-- {
-		other.prepend(values[i], true)
-	}
-	return other
+func (l *List[T]) Prepend(value T) *List[T] {
+	return l.prepend(value, false)
 }
 
 func (l *List[T]) prepend(value T, mutable bool) *List[T] {
@@ -752,18 +744,6 @@ func (m *Map[K, V]) Set(key K, value V) *Map[K, V] {
 	return m.set(key, value, false)
 }
 
-// SetMany returns a map with the keys set to the new values. nil values are allowed.
-//
-// This function will return a new map even if the updated value is the same as
-// the existing value because Map does not track value equality.
-func (m *Map[K, V]) SetMany(entries map[K]V) *Map[K, V] {
-	n := m.clone()
-	for k, v := range entries {
-		n.set(k, v, true)
-	}
-	return n
-}
-
 func (m *Map[K, V]) set(key K, value V, mutable bool) *Map[K, V] {
 	// Set a hasher on the first value if one does not already exist.
 	hasher := m.hasher
@@ -1642,15 +1622,6 @@ func (m *SortedMap[K, V]) Set(key K, value V) *SortedMap[K, V] {
 	return m.set(key, value, false)
 }
 
-// SetMany returns a map with the keys set to the new values.
-func (m *SortedMap[K, V]) SetMany(entries map[K]V) *SortedMap[K, V] {
-	n := m.clone()
-	for k, v := range entries {
-		n.set(k, v, true)
-	}
-	return n
-}
-
 func (m *SortedMap[K, V]) set(key K, value V, mutable bool) *SortedMap[K, V] {
 	// Set a comparer on the first value if one does not already exist.
 	comparer := m.comparer
diff --git a/immutable_test.go b/immutable_test.go
index a878a78..581d4d8 100644
--- a/immutable_test.go
+++ b/immutable_test.go
@@ -223,6 +223,19 @@ func TestList(t *testing.T) {
 		}
 	})
 
+	t.Run("AppendImmutable", func(t *testing.T) {
+		outer_l := NewList[int]()
+		for N := 0; N < 1_000; N++ {
+			l1 := outer_l.Append(0)
+			outer_l.Append(1)
+			if actual := l1.Get(N); actual != 0 {
+				t.Fatalf("Append mutates list with %d elements. Got %d instead of 0", N, actual)
+			}
+
+			outer_l = outer_l.Append(0)
+		}
+	})
+
 	RunRandom(t, "Random", func(t *testing.T, rand *rand.Rand) {
 		l := NewTList()
 		for i := 0; i < 100000; i++ {
@@ -2482,6 +2495,7 @@ func RunRandom(t *testing.T, name string, fn func(t *testing.T, rand *rand.Rand)
 	}
 	t.Run(name, func(t *testing.T) {
 		for i := 0; i < *randomN; i++ {
+			i := i
 			t.Run(fmt.Sprintf("%08d", i), func(t *testing.T) {
 				t.Parallel()
 				fn(t, rand.New(rand.NewSource(int64(i))))
diff --git a/sets.go b/sets.go
index fc30ffb..d610c15 100644
--- a/sets.go
+++ b/sets.go
@@ -14,37 +14,23 @@ type Set[T comparable] struct {
 // Default hasher implementations only exist for int, string, and byte slice types.
 // NewSet can also take some initial values as varargs.
 func NewSet[T comparable](hasher Hasher[T], values ...T) Set[T] {
-	s := Set[T]{
-		m: NewMap[T, struct{}](hasher),
-	}
+	m := NewMap[T, struct{}](hasher)
 	for _, value := range values {
-		s.m.set(value, struct{}{}, true)
+		m = m.set(value, struct{}{}, true)
 	}
-	return s
+	return Set[T]{m}
 }
 
-// Set returns a set containing the new value.
+// Add returns a set containing the new value.
 //
 // This function will return a new set even if the set already contains the value.
-func (s Set[T]) Set(values ...T) Set[T] {
-	n := Set[T]{
-		m: s.m.clone(),
-	}
-	for _, value := range values {
-		n.m.set(value, struct{}{}, true)
-	}
-	return n
+func (s Set[T]) Add(value T) Set[T] {
+	return Set[T]{s.m.Set(value, struct{}{})}
 }
 
 // Delete returns a set with the given key removed.
-func (s Set[T]) Delete(values ...T) Set[T] {
-	n := Set[T]{
-		m: s.m.clone(),
-	}
-	for _, value := range values {
-		n.m.delete(value, true)
-	}
-	return n
+func (s Set[T]) Delete(value T) Set[T] {
+	return Set[T]{s.m.Delete(value)}
 }
 
 // Has returns true when the set contains the given value
@@ -133,37 +119,23 @@ type SortedSet[T comparable] struct {
 // exist for int, string, and byte slice keys.
 // NewSortedSet can also take some initial values as varargs.
 func NewSortedSet[T comparable](comparer Comparer[T], values ...T) SortedSet[T] {
-	s := SortedSet[T]{
-		m: NewSortedMap[T, struct{}](comparer),
-	}
+	m := NewSortedMap[T, struct{}](comparer)
 	for _, value := range values {
-		s.m.set(value, struct{}{}, true)
+		m = m.set(value, struct{}{}, true)
 	}
-	return s
+	return SortedSet[T]{m}
 }
 
-// Set returns a set containing the new value.
+// Add returns a set containing the new value.
 //
 // This function will return a new set even if the set already contains the value.
-func (s SortedSet[T]) Set(values ...T) SortedSet[T] {
-	n := SortedSet[T]{
-		m: s.m.clone(),
-	}
-	for _, value := range values {
-		n.m.set(value, struct{}{}, true)
-	}
-	return n
+func (s SortedSet[T]) Add(value T) SortedSet[T] {
+	return SortedSet[T]{s.m.Set(value, struct{}{})}
 }
 
 // Delete returns a set with the given key removed.
-func (s SortedSet[T]) Delete(values ...T) SortedSet[T] {
-	n := SortedSet[T]{
-		m: s.m.clone(),
-	}
-	for _, value := range values {
-		n.m.delete(value, true)
-	}
-	return n
+func (s SortedSet[T]) Delete(value T) SortedSet[T] {
+	return SortedSet[T]{s.m.Delete(value)}
 }
 
 // Has returns true when the set contains the given value
diff --git a/sets_test.go b/sets_test.go
index b3900fc..ca3aa3d 100644
--- a/sets_test.go
+++ b/sets_test.go
@@ -6,7 +6,8 @@ import (
 
 func TestSetsPut(t *testing.T) {
 	s := NewSet[string](nil)
-	s2 := s.Set("1").Set("1")
+	s2 := s.Add("1").Add("1")
+	s2.Add("2")
 	if s.Len() != 0 {
 		t.Fatalf("Unexpected mutation of set")
 	}
@@ -33,7 +34,7 @@ func TestSetsPut(t *testing.T) {
 
 func TestSetsDelete(t *testing.T) {
 	s := NewSet[string](nil)
-	s2 := s.Set("1")
+	s2 := s.Add("1")
 	s3 := s.Delete("1")
 	if s2.Len() != 1 {
 		t.Fatalf("Unexpected non-mutation of set")
@@ -51,7 +52,7 @@ func TestSetsDelete(t *testing.T) {
 
 func TestSortedSetsPut(t *testing.T) {
 	s := NewSortedSet[string](nil)
-	s2 := s.Set("1").Set("1").Set("0")
+	s2 := s.Add("1").Add("1").Add("0")
 	if s.Len() != 0 {
 		t.Fatalf("Unexpected mutation of set")
 	}
@@ -85,7 +86,7 @@ func TestSortedSetsPut(t *testing.T) {
 
 func TestSortedSetsDelete(t *testing.T) {
 	s := NewSortedSet[string](nil)
-	s2 := s.Set("1")
+	s2 := s.Add("1")
 	s3 := s.Delete("1")
 	if s2.Len() != 1 {
 		t.Fatalf("Unexpected non-mutation of set")