diff --git a/Control/CP/Herbrand/PrologTerm.hs b/Control/CP/Herbrand/PrologTerm.hs
--- a/Control/CP/Herbrand/PrologTerm.hs
+++ b/Control/CP/Herbrand/PrologTerm.hs
@@ -4,6 +4,7 @@
 import Control.CP.Herbrand.Herbrand
 
 data PrologTerm = PTerm String [PrologTerm] | PVar VarId
+     deriving Eq
 
 instance HTerm PrologTerm where
   mkVar           = PVar
diff --git a/monadiccp.cabal b/monadiccp.cabal
--- a/monadiccp.cabal
+++ b/monadiccp.cabal
@@ -1,5 +1,5 @@
 Name:                monadiccp
-Version:             0.4
+Version:             0.4.1
 Description:         Monadic Constraint Programming framework
 License:             BSD3
 License-file:        LICENSE