diff --git a/src/TPDB/CPF/Proof/Read.hs b/src/TPDB/CPF/Proof/Read.hs
--- a/src/TPDB/CPF/Proof/Read.hs
+++ b/src/TPDB/CPF/Proof/Read.hs
@@ -115,7 +115,7 @@
 
 getRule :: Relation -> Cursor -> [ Rule (Term Identifier Symbol) ]
 getRule s c = 
-  ( \ l r -> Rule {lhs=l,relation=s,rhs=r,top=False})
+  ( \ l r -> Rule {lhs=l,relation=s,rhs=r,top=False, original_variable=Nothing})
     <$> (c $/ element "lhs" &/ getTerm) <*> (c $/ element "rhs" &/ getTerm)
 
 getProof :: Cursor -> [ Proof ]
diff --git a/src/TPDB/DP/Transform.hs b/src/TPDB/DP/Transform.hs
--- a/src/TPDB/DP/Transform.hs
+++ b/src/TPDB/DP/Transform.hs
@@ -64,6 +64,7 @@
                                , lhs = tmap Original $ lhs u  
                                , rhs = tmap Original $ rhs u  
                                , top = False
+                               , original_variable = original_variable u
                                } )
            $ rules s
        def = defined s
@@ -83,6 +84,7 @@
                           , lhs = mark_top $ lhs u
                           , rhs = mark_top r 
                           , top = True
+                          , original_variable = original_variable u
                           }
    in RS { signature = map Marked ( S.toList def )
                      ++ map Original ( signature s )
diff --git a/src/TPDB/Data.hs b/src/TPDB/Data.hs
--- a/src/TPDB/Data.hs
+++ b/src/TPDB/Data.hs
@@ -148,7 +148,9 @@
 from_strict_rules :: Bool -> [(t,t)] -> RS i t
 from_strict_rules sep rs =
     RS { rules = map ( \ (l,r) ->
-             Rule { relation = Strict, top = False, lhs = l, rhs = r } ) rs
+             Rule { relation = Strict, top = False, lhs = l, rhs = r
+                  , original_variable = Nothing
+                  } ) rs
        , separate = sep
        }
 
diff --git a/src/TPDB/Data/Rule.hs b/src/TPDB/Data/Rule.hs
--- a/src/TPDB/Data/Rule.hs
+++ b/src/TPDB/Data/Rule.hs
@@ -6,14 +6,14 @@
 data Relation = Strict |  Weak | Equal deriving ( Eq, Ord, Typeable, Show )
 
 data Rule a = Rule
-  { lhs :: a, rhs :: a 
-  , relation :: Relation
-  , top :: Bool
-  -- TPDC (XTC) represents SRS as TRS,
+  { lhs :: !a, rhs :: !a 
+  , relation :: !Relation
+  , top :: !Bool
+  -- TPDB (XTC) represents SRS as TRS,
   -- e.g.,  "ab -> ba" is "a(b(x)) -> b(a(x))",
   -- and when we convert back (as we need for CPF),
   -- need to use the original variable in the rule
-  , original_variable :: Maybe Identifier 
+  , original_variable :: !(Maybe Identifier)
   }
     deriving ( Eq, Ord, Typeable )
 
diff --git a/src/TPDB/XTC/Read.hs b/src/TPDB/XTC/Read.hs
--- a/src/TPDB/XTC/Read.hs
+++ b/src/TPDB/XTC/Read.hs
@@ -115,6 +115,6 @@
 
 getRule :: Relation -> Cursor -> [ Rule (Term Identifier Identifier) ]
 getRule s c = 
-  ( \ l r -> Rule {lhs=l,relation=s,rhs=r,top=False})
+  ( \ l r -> Rule {lhs=l,relation=s,rhs=r,top=False,original_variable=Nothing})
     <$> (c $/ element "lhs" &/ getTerm) <*> (c $/ element "rhs" &/ getTerm)
 
diff --git a/tpdb.cabal b/tpdb.cabal
--- a/tpdb.cabal
+++ b/tpdb.cabal
@@ -1,7 +1,7 @@
 Cabal-Version: 3.0
 
 Name: tpdb
-Version: 2.7.1
+Version: 2.7.2
 
 Author: Alexander Bau, Johannes Waldmann
 Maintainer: Johannes Waldmann