X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;ds=sidebyside;f=helm%2Fsoftware%2Fcomponents%2Ftactics%2FprimitiveTactics.ml;h=192460633d7577ff26a18e40d2d8ac4e8f699651;hb=abd2098b6c4a40b36bb4b950c607eb4b4a7852bc;hp=9baf829ea940d2bad3c61d71ebfdea8781043f34;hpb=4104453c74bbff05f95003f8d6239f873d1adbf9;p=helm.git

diff --git a/helm/software/components/tactics/primitiveTactics.ml b/helm/software/components/tactics/primitiveTactics.ml
index 9baf829ea..192460633 100644
--- a/helm/software/components/tactics/primitiveTactics.ml
+++ b/helm/software/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 =