diff -r cfd8d2304e9e -r 15f01efc034b src/zero.rs
--- a/src/zero.rs	Sat Dec 07 21:54:59 2024 -0500
+++ b/src/zero.rs	Sun Dec 15 01:10:52 2024 -0500
@@ -2,7 +2,7 @@
 Implementation of the the constant zero function on a manifold.
 */
 
-use alg_tools::mapping::Apply;
+use alg_tools::mapping::{Mapping, Instance};
 use crate::manifold::ManifoldPoint;
 use crate::fb::{Grad, Desc, Prox};
 use std::marker::PhantomData;
@@ -19,21 +19,14 @@
     }
 }
 
-impl<M : ManifoldPoint> Apply<M> for ZeroFn<M> {
-    type Output = f64;
+impl<M : ManifoldPoint> Mapping<M> for ZeroFn<M> {
+    type Codomain = f64;
 
-    fn apply(&self, _x : M) -> Self::Output {
+    fn apply<I : Instance<M>>(&self, _x : I) -> Self::Codomain {
         0.0
     }
 }
 
-impl<'a, M : ManifoldPoint> Apply<&'a M> for ZeroFn<M> {
-    type Output = f64;
-
-    fn apply(&self, _x : &'a M) -> Self::Output {
-        0.0
-    }
-}
 
 impl<M : ManifoldPoint> Desc<M> for ZeroFn<M> {
     fn desc(&self, _τ : f64, x : M) -> M {