diff --git a/src/prolog/copier.rs b/src/prolog/copier.rs
index 6bff84e5..f108d15c 100644
--- a/src/prolog/copier.rs
+++ b/src/prolog/copier.rs
@@ -12,12 +12,6 @@ pub trait CopierTarget
     fn deref(&self, Addr) -> Addr;
     fn stack(&mut self) -> &mut AndStack;
 
-    //TODO: extend this so include a boundary() function which is constant!!
-    // this will return self.h. the threshold() will be used to set the addresses
-    // contained within the terms so that the offsets match those of the heap
-    // to be truncated by BLOCK, ie. starting at the BLOCK.H value. This should
-    // allow us to get around the latest bug.
-
     // duplicate_term(L1, L2) uses Cheney's algorithm to copy the term at
     // L1 to L2. forwarding_terms is kept to restore the innards of L1
     // after it's been copied to L2.