From ce87e338529f4dd174f1c870b83162bac6d2b9ae Mon Sep 17 00:00:00 2001
From: Matthieu Sozeau
Date: Thu, 8 Mar 2018 07:23:03 -0300
Subject: Leave cumul constructor universes as is during unif

if we cannot coerce one constructor type to the other. By invariant
they have a common supertype
---
 pretyping/evarconv.ml | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/pretyping/evarconv.ml b/pretyping/evarconv.ml
index 3c8acb1a78..fe2e86a482 100644
--- a/pretyping/evarconv.ml
+++ b/pretyping/evarconv.ml
@@ -532,12 +532,13 @@ and evar_eqappr_x ?(rhs_is_already_stuck = false) ts env evd pbty
                 begin
                   (** Both constructors should be liftable to the same supertype
                       at which we compare them, but we don't have access to that type in
-                      untyped unification. We hence enforce that one is lower than the other.
-                      Note the criterion is more relaxed in conversion. *)
+                      untyped unification. We hence try to enforce that one is lower
+                      than the other, also unifying more universes in the process.
+                      If this fails we just leave the universes as is, as in conversion. *)
                   try Success (check_leq_inductives evd cumi u u')
                   with Univ.UniverseInconsistency _ ->
                     try Success (check_leq_inductives evd cumi u' u)
-                    with Univ.UniverseInconsistency e -> UnifFailure (evd, UnifUnivInconsistency e)
+                    with Univ.UniverseInconsistency e -> Success evd
                 end
             end
         in
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