diff --git a/src/GF/Command/TreeOperations.hs b/src/GF/Command/TreeOperations.hs
index 0ff6ac682..da7399615 100644
--- a/src/GF/Command/TreeOperations.hs
+++ b/src/GF/Command/TreeOperations.hs
@@ -5,7 +5,7 @@ module GF.Command.TreeOperations (
   ) where
 
 import GF.Compile.TypeCheck
-import PGF (compute)
+import PGF (compute,paraphrase)
 
 -- for conversions
 import PGF.Data
@@ -24,6 +24,8 @@ allTreeOps :: PGF -> [(String,(String,TreeOp))]
 allTreeOps pgf = [
    ("compute",("compute by using semantic definitions (def)",
       map (compute pgf))),
+   ("paraphrase",("paraphrase by using semantic definitions (def)",
+      concatMap (paraphrase pgf))),
    ("smallest",("sort trees from smallest to largest, in number of nodes",
       smallest)),
    ("typecheck",("type check and solve metavariables; reject if incorrect",
diff --git a/src/PGF.hs b/src/PGF.hs
index 31801a54f..c078bf3bf 100644
--- a/src/PGF.hs
+++ b/src/PGF.hs
@@ -44,7 +44,7 @@ module PGF(
            parse, canParse, parseAllLang, parseAll,
            
            -- ** Evaluation
-           tree2expr, expr2tree, compute,
+           tree2expr, expr2tree, compute, paraphrase,
            
            -- ** Word Completion (Incremental Parsing)
            complete,
@@ -59,6 +59,7 @@ import PGF.CId
 import PGF.Linearize
 import PGF.Generate
 import PGF.AbsCompute
+import PGF.Paraphrase
 import PGF.Macros
 import PGF.Data
 import PGF.Expr
diff --git a/src/PGF/Paraphrase.hs b/src/PGF/Paraphrase.hs
new file mode 100644
index 000000000..6e20e1e18
--- /dev/null
+++ b/src/PGF/Paraphrase.hs
@@ -0,0 +1,103 @@
+----------------------------------------------------------------------
+-- |
+-- Module      : Paraphrase
+-- Maintainer  : AR
+-- Stability   : (stable)
+-- Portability : (portable)
+--
+-- generate parapharases with def definitions.
+--
+-- modified from src GF computation
+-----------------------------------------------------------------------------
+
+module PGF.Paraphrase (
+  paraphrase,
+  paraphraseN
+  ) where
+
+import PGF.Data
+import PGF.Macros (lookDef,isData)
+import PGF.Expr
+import PGF.CId
+
+import Data.List
+import qualified Data.Map as Map
+
+paraphrase :: PGF -> Tree -> [Tree]
+paraphrase pgf = nub . paraphraseN 2 pgf
+
+paraphraseN :: Int -> PGF -> Tree -> [Tree]
+paraphraseN 0 _ t = [t]
+paraphraseN i pgf t = 
+  step i t ++ [Fun g ts' | Fun g ts <- step (i-1) t, ts' <- sequence (map par ts)]
+ where
+  par = paraphraseN (i-1) pgf 
+  step 0 t = [t]
+  step i t = let stept = step (i-1) t in stept ++ concat [def u | u <- stept]
+  def = fromDef pgf
+
+fromDef :: PGF -> Tree -> [Tree]
+fromDef pgf t@(Fun f ts) = defDown t ++ defUp t where
+  defDown t = [subst g u | let equ = equsFrom f, (u,g) <- match equ ts]
+  defUp   t = [subst g u | equ <- equsTo   f, (u,g) <- match [equ] ts]
+
+  equsFrom f = [(ps,d) | Just equs <- [lookup f equss], (Fun _ ps,d) <- equs]
+
+  equsTo f  = [c | (_,equs) <- equss, c <- casesTo f equs]
+
+  casesTo f equs = 
+    [(ps,p) | (p,d@(Fun g ps)) <- equs, g==f, 
+              isClosed d || (length equs == 1 && isLinear d)]
+
+  equss = [(f,[(Fun f (map expr2tree ps), expr2tree d) | (Equ ps d) <- eqs]) | 
+                       (f,(_,EEq eqs)) <- Map.assocs (funs (abstract pgf))]
+
+subst :: Subst -> Tree -> Tree
+subst g e = case e of
+  Fun f ts -> Fun f (map substg ts)
+  Var x -> maybe e id $ lookup x g
+  _ -> e
+ where
+  substg = subst g
+
+type Subst = [(CId,Tree)]
+
+-- this applies to pattern, hence don't need to consider abstractions
+isClosed :: Tree -> Bool
+isClosed t = case t of
+  Fun _ ts -> all isClosed ts
+  Var _ -> False
+  _ -> True
+
+-- this applies to pattern, hence don't need to consider abstractions
+isLinear :: Tree -> Bool
+isLinear = nodup . vars where
+  vars t = case t of
+    Fun _ ts -> concatMap vars ts
+    Var x -> [x]
+    _ -> []
+  nodup = all ((<2) . length) . group . sort
+
+
+-- special version of AbsCompute.findMatch, working on Tree
+
+match :: [([Tree],Tree)] -> [Tree] -> [(Tree, Subst)]
+match cases terms = case cases of
+  [] -> []
+  (patts,_):_ | length patts /= length terms -> []
+  (patts,val):cc -> case mapM tryMatch (zip patts terms) of
+     Just substs -> return (val, concat substs)
+     _           -> match cc terms
+ where  
+  tryMatch (p,t) = case (p, t) of
+    (Var x,     _) | notMeta t  -> return [(x,t)]
+    (Fun p pp, Fun f tt) | p == f && length pp == length tt -> do
+         matches <- mapM tryMatch (zip pp tt)
+         return (concat matches)
+    _ -> if p==t then return [] else Nothing
+
+  notMeta e = case e of
+    Meta _   -> False
+    Fun f ts -> all notMeta ts  
+    _ -> True
+