X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;ds=sidebyside;f=components%2Ftactics%2FprimitiveTactics.ml;h=192460633d7577ff26a18e40d2d8ac4e8f699651;hb=c61fbff7b7296b56aa5313823bc2df4d344c9ce6;hp=9baf829ea940d2bad3c61d71ebfdea8781043f34;hpb=45d71beffd253ffd767a9afbfcec5c4f44afd8a8;p=helm.git

diff --git a/components/tactics/primitiveTactics.ml b/components/tactics/primitiveTactics.ml
index 9baf829ea..192460633 100644
--- a/components/tactics/primitiveTactics.ml
+++ b/components/tactics/primitiveTactics.ml
@@ -419,8 +419,17 @@ let letin_tac ?(mk_fresh_name_callback=FreshNamesGenerator.mk_fresh_name ~subst:
  =
   let module C = Cic in
    let curi,metasenv,pbo,pty = proof in
+   (* occur check *)
+   let occur i t =
+     let m = CicUtil.metas_of_term t in 
+     List.exists (fun (j,_) -> i=j) m
+   in
    let metano,context,ty = CicUtil.lookup_meta goal metasenv in
-    let _,_ = (* TASSI: FIXME *)
+   if occur metano term then
+     raise 
+       (ProofEngineTypes.Fail (lazy
+         "You can't letin a term containing the current goal"));
+    let _,_ =
       CicTypeChecker.type_of_aux' metasenv context term CicUniv.empty_ugraph in
      let newmeta = new_meta_of_proof ~proof in
      let fresh_name =