Major code semplification and bugs removed (thanks to a better invariant):

small_delta_step always put the terms in WHNF, even if it can do that with delta > 0.
Terms in WHNF, delta=0 that are not head-alpha convertible and tail-machine convertible
are not convertible.

diff --git a/helm/software/components/ng_kernel/nCicReduction.ml b/helm/software/components/ng_kernel/nCicReduction.ml
index 99afc2aa8b27ad0822822480cafa9a730faa366f..6f94e4a771fe3c8e0e443254b61bd2c8481e8bdc 100644 (file)
--- a/helm/software/components/ng_kernel/nCicReduction.ml
+++ b/helm/software/components/ng_kernel/nCicReduction.ml
@@ -554,23 +554,19 @@ let are_convertible whd ?(subst=[])  =
      true
    else
      let height_of = function
-      | NCic.Const (NReference.Ref (_,NReference.Def h)) -> h
-      | NCic.Const (NReference.Ref (_,NReference.Fix (_,_,h))) -> h
-      | NCic.Appl(NCic.Const(NReference.Ref(_,NReference.Def h))::_) -> h
+      | NCic.Const (NReference.Ref (_,NReference.Def h)) 
+      | NCic.Const (NReference.Ref (_,NReference.Fix (_,_,h))) 
+      | NCic.Appl(NCic.Const(NReference.Ref(_,NReference.Def h))::_) 
       | NCic.Appl(NCic.Const(NReference.Ref(_,NReference.Fix (_,_,h)))::_) -> h
       | _ -> 0
      in
-     let small_delta_step (k1,env1,t1,s1 as m1) (k2,env2,t2,s2 as m2) = 
-       let h1 = height_of t1 and h2 = height_of t2 in
-       if h1 > h2 then
-         R.reduce ~delta:h2 ~subst context (k1,env1,t1,s1), m2, h2
-       else if h1 < h2 then
-         m1, R.reduce ~delta:h1 ~subst context (k2,env2,t2,s2), h1
-       else
-         let delta = max 0 (h1-1) in
-         R.reduce ~delta ~subst context (k1,env1,t1,s1),
-         R.reduce ~delta ~subst context (k2,env2,t2,s2),
-         delta
+     let small_delta_step (_,_,t1,_ as m1) (_,_,t2,_ as m2) = 
+       let h1 = height_of t1 in 
+       let h2 = height_of t2 in
+       let delta = if h1 = h2 then max 0 (h1 -1) else min h1 h2 in
+       R.reduce ~delta ~subst context m1,
+       R.reduce ~delta ~subst context m2,
+       delta
      in
      let rec convert_machines ((k1,e1,t1,s1 as m1),(k2,e2,t2,s2 as m2),delta) =
        (alpha_eq test_eq_only
@@ -582,11 +578,9 @@ let are_convertible whd ?(subst=[])  =
              convert_machines (small_delta_step t1 t2))
            (List.combine s1 s2)
         with Invalid_argument _ -> false) || 
-       (let red delta = R.reduce ~delta ~subst context in
-        if delta = 0 then
-          alpha_eq test_eq_only (R.unwind (red 0 m1)) (R.unwind (red 0 m2))
-        else
+       (delta > 0 &&
           let delta = delta - 1 in 
+          let red = R.reduce ~delta ~subst context in
           convert_machines (red delta m1,red delta m2,delta))
      in
      convert_machines (small_delta_step (0,[],t1,[]) (0,[],t2,[]))