From fdd6a17b272995237c9f95fc465bb1ff6871bedc Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Thu, 16 Jul 2015 22:53:10 +0200
Subject: Refining 71def2f8 on too strong occur-check limiting evar-evar
 unification in tactics.

The relaxing of occur-check was ok but was leading trivial problems of
the form ?X[?Meta] = ?X[?Meta] to enter a complex Evar-ization into
?X[?Meta] = ?X[?Y], ?Meta:=?Y which consider_remaining_unif_problems
was not any more able to deal with.

Doing quick: treat the trivial cases ?X[args] = ?X[args] in an ad hoc way,
so that it behaves as if the occur-check had not been restricted.
---
 pretyping/unification.ml | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

(limited to 'pretyping')

diff --git a/pretyping/unification.ml b/pretyping/unification.ml
index b5fe5d0b6d..24e06007e9 100644
--- a/pretyping/unification.ml
+++ b/pretyping/unification.ml
@@ -676,7 +676,11 @@ let rec unify_0_with_initial_metas (sigma,ms,es as subst) conv_at_top env cv_pb
 	| Evar (evk,_ as ev), Evar (evk',_)
             when not (Evar.Set.mem evk flags.frozen_evars)
               && Evar.equal evk evk' ->
-	    sigma,metasubst,((curenv,ev,cN)::evarsubst)
+            let sigma',b = constr_cmp cv_pb sigma flags cM cN in
+            if b then
+	      sigma',metasubst,evarsubst
+            else
+	      sigma,metasubst,((curenv,ev,cN)::evarsubst)
 	| Evar (evk,_ as ev), _
             when not (Evar.Set.mem evk flags.frozen_evars) 
 	      && not (occur_evar evk cN) ->
-- 
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