diff -r f248e1434c3b -r df9628092285 src/manifold.rs
--- a/src/manifold.rs	Sat Oct 19 10:46:13 2024 -0500
+++ b/src/manifold.rs	Mon Oct 21 08:44:23 2024 -0500
@@ -14,5 +14,8 @@
 
     /// Distance to `other`
     fn dist_to(&self, other : &Self) -> f64;
+
+    /// Return the zero tangent at `self`.
+    fn tangent_origin(&self) -> Self::Tangent;
 }