diff -r dccf609cd020 -r a5ee4bfb0b87 src/mapping/dataterm.rs
--- a/src/mapping/dataterm.rs	Mon Dec 08 15:23:42 2025 -0500
+++ b/src/mapping/dataterm.rs	Thu Jan 15 16:12:47 2026 -0500
@@ -112,12 +112,11 @@
     F: Float,
     X: Space,
     Y: Space + Instance<Y> + for<'a> Sub<&'a Y, Output = Y>,
-    //<A as Mapping<X>>::Codomain: Euclidean<F>,
     A: Linear<X, Codomain = Y> + Preadjointable<X, G::DerivativeDomain>,
     G::DerivativeDomain: Instance<G::DerivativeDomain>,
     A::PreadjointCodomain: ClosedSpace,
-    //<<A as Mapping<X>>::Codomain as Euclidean<F>>::Output: Instance<<A as Mapping<X>>::Codomain>,
     G: DifferentiableMapping<Y, Codomain = F>,
+    Self: Mapping<X, Codomain = F>,
 {
     type Derivative = A::PreadjointCodomain;
 
@@ -129,7 +128,13 @@
         //self.opA.preadjoint().apply(self.opA.apply(x) - self.b)
         self.opA
             .preadjoint()
-            .apply(self.g.diff_ref().apply(self.opA.apply(x) - &self.b))
+            .apply(self.g.differential(self.opA.apply(x) - &self.b))
+    }
+
+    fn apply_and_differential_impl<I: Instance<X>>(&self, x: I) -> (F, Self::Derivative) {
+        let j = self.opA.apply(x) - &self.b;
+        let (v, d) = self.g.apply_and_differential(j);
+        (v, self.opA.preadjoint().apply(d))
     }
 }