diff --git a/sledge/src/trm.ml b/sledge/src/trm.ml
index 92daf7b49..693d035f9 100644
--- a/sledge/src/trm.ml
+++ b/sledge/src/trm.ml
@@ -390,6 +390,8 @@ type arith = Arith.t
 
 include Trm
 
+let pp_diff fs (x, y) = Format.fprintf fs "-- %a ++ %a" pp x pp y
+
 (** Construct *)
 
 (* variables *)
diff --git a/sledge/src/trm.mli b/sledge/src/trm.mli
index 10a8ca329..5fd7dcafe 100644
--- a/sledge/src/trm.mli
+++ b/sledge/src/trm.mli
@@ -42,6 +42,8 @@ module Arith :
   Arithmetic.S with type var := Var.t with type trm := t with type t = arith
 
 val ppx : Var.strength -> t pp
+val pp : t pp
+val pp_diff : (t * t) pp
 
 (** Construct *)