diff --git a/fj-operations/src/difference_2d.rs b/fj-operations/src/difference_2d.rs
index 89178c598..bf0cd58fe 100644
--- a/fj-operations/src/difference_2d.rs
+++ b/fj-operations/src/difference_2d.rs
@@ -16,8 +16,12 @@ impl ToShape for fj::Difference2d {
 
         let mut shape = Shape::new();
 
-        let [mut a, mut b] = [&self.a(), &self.b()]
-            .map(|shape| shape.to_shape(tolerance, debug_info));
+        // Can be cleaned up, once `each_ref` is stable:
+        // https://doc.rust-lang.org/std/primitive.array.html#method.each_ref
+        let [a, b] = self.shapes();
+        let shapes = [&a, &b];
+        let [mut a, mut b] =
+            shapes.map(|shape| shape.to_shape(tolerance, debug_info));
 
         // Check preconditions.
         //
@@ -76,7 +80,7 @@ impl ToShape for fj::Difference2d {
         // This is a conservative estimate of the bounding box: It's never going
         // to be bigger than the bounding box of the original shape that another
         // is being subtracted from.
-        self.a().bounding_volume()
+        self.shapes()[0].bounding_volume()
     }
 }
 
diff --git a/fj-operations/src/sweep.rs b/fj-operations/src/sweep.rs
index 15f816fc8..0a2dab176 100644
--- a/fj-operations/src/sweep.rs
+++ b/fj-operations/src/sweep.rs
@@ -10,7 +10,7 @@ impl ToShape for fj::Sweep {
             self.shape().to_shape(tolerance, debug_info),
             Vector::from([0., 0., self.length()]),
             tolerance,
-            self.color(),
+            self.shape().color(),
         )
     }
 
diff --git a/fj/src/shape_2d.rs b/fj/src/shape_2d.rs
index 50aae3b8f..f5116d824 100644
--- a/fj/src/shape_2d.rs
+++ b/fj/src/shape_2d.rs
@@ -84,32 +84,23 @@ impl From<Circle> for Shape2d {
 #[derive(Clone, Debug)]
 #[repr(C)]
 pub struct Difference2d {
-    /// The original shape
-    a: Shape2d,
-
-    /// The shape being subtracted
-    b: Shape2d,
+    shapes: [Shape2d; 2],
 }
 
 impl Difference2d {
     /// Create a `Difference2d` from two shapes
-    pub fn from_objects(a: Shape2d, b: Shape2d) -> Self {
-        Self { a, b }
+    pub fn from_shapes(shapes: [Shape2d; 2]) -> Self {
+        Self { shapes }
     }
 
     /// Get the rendering color of the larger object in RGBA
     pub fn color(&self) -> [u8; 4] {
-        self.a.color()
-    }
-
-    /// Access the original shape
-    pub fn a(&self) -> &Shape2d {
-        &self.a
+        self.shapes[0].color()
     }
 
-    /// Access the shape being subtracted
-    pub fn b(&self) -> &Shape2d {
-        &self.b
+    /// Access the shapes that make up the difference
+    pub fn shapes(&self) -> &[Shape2d; 2] {
+        &self.shapes
     }
 }
 
diff --git a/fj/src/shape_3d.rs b/fj/src/shape_3d.rs
index be6ae2ba1..2962afc27 100644
--- a/fj/src/shape_3d.rs
+++ b/fj/src/shape_3d.rs
@@ -113,11 +113,6 @@ impl Sweep {
     pub fn length(&self) -> f64 {
         self.length
     }
-
-    /// Access the color of the shape being swept
-    pub fn color(&self) -> [u8; 4] {
-        self.shape().color()
-    }
 }
 
 impl From<Sweep> for Shape {
diff --git a/fj/src/syntax.rs b/fj/src/syntax.rs
index 0422cb0ce..6dee78e22 100644
--- a/fj/src/syntax.rs
+++ b/fj/src/syntax.rs
@@ -24,7 +24,7 @@ where
         let a = self.clone().into();
         let b = other.clone().into();
 
-        crate::Difference2d::from_objects(a, b)
+        crate::Difference2d::from_shapes([a, b])
     }
 }
 
@@ -53,32 +53,6 @@ where
     }
 }
 
-/// Convenient syntax to create an [`fj::Transform`]
-///
-/// [`fj::Transform`]: crate::Transform
-pub trait Rotate {
-    /// Create a rotation
-    ///
-    /// Create a rotation that rotates `shape` by `angle` around an axis defined
-    /// by `axis`.
-    fn rotate(&self, axis: [f64; 3], angle: f64) -> crate::Transform;
-}
-
-impl<T> Rotate for T
-where
-    T: Clone + Into<crate::Shape3d>,
-{
-    fn rotate(&self, axis: [f64; 3], angle: f64) -> crate::Transform {
-        let shape = self.clone().into();
-        crate::Transform {
-            shape,
-            axis,
-            angle,
-            offset: [0.; 3],
-        }
-    }
-}
-
 /// Convenient syntax to create an [`fj::Sketch`]
 ///
 /// [`fj::Sketch`]: crate::Sketch
@@ -120,17 +94,33 @@ where
 /// Convenient syntax to create an [`fj::Transform`]
 ///
 /// [`fj::Transform`]: crate::Transform
-pub trait Translate {
+pub trait Transform {
+    /// Create a rotation
+    ///
+    /// Create a rotation that rotates `shape` by `angle` around an axis defined
+    /// by `axis`.
+    fn rotate(&self, axis: [f64; 3], angle: f64) -> crate::Transform;
+
     /// Create a translation
     ///
     /// Create a translation that translates `shape` by `offset`.
     fn translate(&self, offset: [f64; 3]) -> crate::Transform;
 }
 
-impl<T> Translate for T
+impl<T> Transform for T
 where
     T: Clone + Into<crate::Shape3d>,
 {
+    fn rotate(&self, axis: [f64; 3], angle: f64) -> crate::Transform {
+        let shape = self.clone().into();
+        crate::Transform {
+            shape,
+            axis,
+            angle,
+            offset: [0.; 3],
+        }
+    }
+
     fn translate(&self, offset: [f64; 3]) -> crate::Transform {
         let shape = self.clone().into();
         crate::Transform {
diff --git a/models/star/src/lib.rs b/models/star/src/lib.rs
index 8367c1544..70f200e31 100644
--- a/models/star/src/lib.rs
+++ b/models/star/src/lib.rs
@@ -53,7 +53,7 @@ pub extern "C" fn model(args: &HashMap<String, String>) -> fj::Shape {
     let outer = fj::Sketch::from_points(outer).with_color([0, 255, 0, 200]);
     let inner = fj::Sketch::from_points(inner);
 
-    let footprint = fj::Difference2d::from_objects(outer.into(), inner.into());
+    let footprint = fj::Difference2d::from_shapes([outer.into(), inner.into()]);
 
     let star = fj::Sweep::from_shape_and_length(footprint.into(), h);