diff --git a/src/core/expr_intf.ml b/src/core/expr_intf.ml
index 685e46ff..a718e935 100644
--- a/src/core/expr_intf.ml
+++ b/src/core/expr_intf.ml
@@ -16,7 +16,6 @@ module type S = sig
     type t
     val hash : t -> int
     val equal : t -> t -> bool
-    val compare : t -> t -> int
     val print : Format.formatter -> t -> unit
   end
 
@@ -25,7 +24,6 @@ module type S = sig
     type t
     val hash : t -> int
     val equal : t -> t -> bool
-    val compare : t -> t -> int
     val print : Format.formatter -> t -> unit
   end
 
diff --git a/src/core/formula_intf.ml b/src/core/formula_intf.ml
index cd6583e7..360fde32 100644
--- a/src/core/formula_intf.ml
+++ b/src/core/formula_intf.ml
@@ -34,8 +34,7 @@ module type S = sig
 
   val hash : t -> int
   val equal : t -> t -> bool
-  val compare : t -> t -> int
-  (** Usual hash and comparison functions. Given to Map and Hash functors. *)
+  (** Usual hash and comparison functions. Given to Hashtbl functors. *)
 
   val print : Format.formatter -> t -> unit
   (** Printing function used for debugging. *)