diff --git a/src/ToolboxInput.ml b/src/ToolboxInput.ml
index 402be7a8c20f29882e947c96de676e52d4bbc095..0825769a9a59edd9749b1560f9f0a2775411095f 100644
--- a/src/ToolboxInput.ml
+++ b/src/ToolboxInput.ml
@@ -24,7 +24,6 @@ module type INPUT = sig
 
   class virtual ['self] map : object ('self)
     method private virtual extend : 'env -> 'bn1 -> 'env * 'bn2
-    method private virtual lookup : 'env -> 'bn1 -> 'bn2
     method private virtual visit_'fn : 'env -> 'fn1 -> 'fn2
     method visit_term : 'env -> ('bn1, 'fn1) term -> ('bn2, 'fn2) term
     method private visit_TVar : 'env -> 'fn1 -> ('bn2, 'fn2) term