diff -r 2f1798c65fd6 -r c4e394a9c84c src/bisection_tree/either.rs
--- a/src/bisection_tree/either.rs	Mon Sep 01 00:04:22 2025 -0500
+++ b/src/bisection_tree/either.rs	Mon Sep 01 13:51:03 2025 -0500
@@ -3,7 +3,9 @@
 
 use crate::iter::{MapF, MapZ, Mappable};
 use crate::loc::Loc;
-use crate::mapping::{DifferentiableImpl, DifferentiableMapping, Instance, Mapping, Space};
+use crate::mapping::{
+    ClosedSpace, DifferentiableImpl, DifferentiableMapping, Instance, Mapping, Space,
+};
 use crate::sets::Cube;
 use crate::types::*;
 
@@ -192,7 +194,7 @@
 
 impl<F, S1, S2, X> Mapping<X> for EitherSupport<S2, S1>
 where
-    F: Space,
+    F: ClosedSpace,
     X: Space,
     S1: Mapping<X, Codomain = F>,
     S2: Mapping<X, Codomain = F>,
@@ -210,8 +212,8 @@
 
 impl<X, S1, S2, O> DifferentiableImpl<X> for EitherSupport<S2, S1>
 where
-    O: Space,
-    X: Space,
+    O: ClosedSpace,
+    X: ClosedSpace,
     S1: DifferentiableMapping<X, DerivativeDomain = O>,
     S2: DifferentiableMapping<X, DerivativeDomain = O>,
 {