From fd2e9fd5f859f729765706f1f56df0fa080c0513 Mon Sep 17 00:00:00 2001
From: Matthieu Sozeau
Date: Thu, 4 Jan 2018 05:40:08 -0800
Subject: Relax conversion of constructors according to the pCuIC model

- Nothing to check in conversion as they have a common supertype
  by typing.
- In inference, enforce that one is lower than the other.
---
 pretyping/evarconv.ml | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

(limited to 'pretyping')

diff --git a/pretyping/evarconv.ml b/pretyping/evarconv.ml
index 0a63985bf1..3c8acb1a78 100644
--- a/pretyping/evarconv.ml
+++ b/pretyping/evarconv.ml
@@ -530,8 +530,14 @@ and evar_eqappr_x ?(rhs_is_already_stuck = false) ts env evd pbty
                 UnifFailure (evd, NotSameHead)
               else
                 begin
-                  let evd' = check_leq_inductives evd cumi u u' in
-                  Success (check_leq_inductives evd' cumi u' u)
+                  (** 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. *)
+                  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)
                 end
             end
         in
-- 
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