diff -r e7f1cb4bec78 -r 103aa137fcb2 src/mapping.rs
--- a/src/mapping.rs	Tue Apr 29 00:03:12 2025 -0500
+++ b/src/mapping.rs	Tue Apr 29 07:55:18 2025 -0500
@@ -9,6 +9,7 @@
 use crate::types::{ClosedMul, Float, Num};
 use std::borrow::Cow;
 use std::marker::PhantomData;
+use std::ops::Mul;
 
 /// A mapping from `Domain` to `Self::Codomain`.
 pub trait Mapping<Domain: Space> {
@@ -283,8 +284,39 @@
     }
 }
 
+/// Helper trait for implementing [`DifferentiableMapping`]
+impl<S, T, X, E, Y> DifferentiableImpl<X> for Composition<S, T, E>
+where
+    X: Space,
+    T: DifferentiableImpl<X> + Mapping<X>,
+    S: DifferentiableImpl<T::Codomain>,
+    E: Copy,
+    //Composition<S::Derivative, T::Derivative, E>: Space,
+    S::Derivative: Mul<T::Derivative, Output = Y>,
+    Y: Space,
+{
+    //type Derivative = Composition<S::Derivative, T::Derivative, E>;
+    type Derivative = Y;
+
+    /// Compute the differential of `self` at `x`, consuming the input.
+    fn differential_impl<I: Instance<X>>(&self, x: I) -> Self::Derivative {
+        // Composition {
+        //     outer: self
+        //         .outer
+        //         .differential_impl(self.inner.apply(x.ref_instance())),
+        //     inner: self.inner.differential_impl(x),
+        //     intermediate_norm_exponent: self.intermediate_norm_exponent,
+        // }
+        self.outer
+            .differential_impl(self.inner.apply(x.ref_instance()))
+            * self.inner.differential_impl(x)
+    }
+}
+
 mod quadratic;
 pub use quadratic::Quadratic;
+mod dataterm;
+pub use dataterm::DataTerm;
 
 /// Trait for indicating that `Self` is Lipschitz with respect to the (semi)norm `D`.
 pub trait Lipschitz<M> {