From 25c82d55497db43bf2cd131f10d2ef366758bbe1 Mon Sep 17 00:00:00 2001
From: Matthieu Sozeau
Date: Fri, 18 Nov 2016 13:25:05 +0100
Subject: Fix UGraph.check_eq!

Universes are kept in normal form w.r.t. equality but not the <=
relation, so the previous check worked almost always but was actually
too strict! In cases like (max(Set,u) = u) when u is declared >= Set it
was failing to find an equality. Applying the KISS principle:
u = v <-> u <= v /\ v <= u.

Fix invariant breakage that triggered the discovery of the check_eq bug as well. No algebraic universes should appear in a term position (on the left of
a colon in a typing judgment), this was not the case when an algebraic
universe instantiated an evar that appeared in the term. We force their
universe variable status to change in refresh_universes to avoid this.

Fix ind sort inference: Use syntactic universe equality for inductive
sort inference instead of check_leq (which now correctly takes
constraints into account) and simplify code
---
 engine/evd.ml | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'engine/evd.ml')

diff --git a/engine/evd.ml b/engine/evd.ml
index aa91fc5222..a6b6f742b7 100644
--- a/engine/evd.ml
+++ b/engine/evd.ml
@@ -854,6 +854,13 @@ let is_eq_sort s1 s2 =
       if Univ.Universe.equal u1 u2 then None
       else Some (u1, u2)
 
+(* Precondition: l is not defined in the substitution *)
+let universe_rigidity evd l =
+  let uctx = evd.universes in
+  if Univ.LSet.mem l (Univ.ContextSet.levels (UState.context_set uctx)) then
+    UnivFlexible (Univ.LSet.mem l (UState.algebraics uctx))
+  else UnivRigid
+
 let normalize_universe evd =
   let vars = ref (UState.subst evd.universes) in
   let normalize = Universes.normalize_universe_opt_subst vars in
-- 
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