Allow using cumulativity without forcing strict constraints.

Previously [fun x : Ind@{i} => x : Ind@{j}] with Ind some cumulative
inductive would try to generate a constraint [i = j] and use
cumulativity only if this resulted in an inconsistency. This is
confusingly different from the behaviour with [Type] and means
cumulativity can only be used to lift between universes related by
strict inequalities. (This isn't a kernel restriction so there might
be some workaround to send the kernel the right constraints, but
not in a nice way.)

See modified test for more details of what is now possible.

Technical notes:

When universe constraints were inferred by comparing the shape of
terms without reduction, cumulativity was not used and so too-strict
equality constraints were generated. Then in order to use cumulativity
we had to make this comparison fail to fall back to full conversion.

When unifiying 2 instances of a cumulative inductive type, if there
are any Irrelevant universes we try to unify them if they are
flexible.

1 files changed, 1 insertions, 1 deletions

diff --git a/library/globnames.mli b/library/globnames.mli
index 017b7386d..f2b88b870 100644
--- a/library/globnames.mli
+++ b/library/globnames.mli
@@ -14,7 +14,7 @@ open Constr
 open Mod_subst
 
 (** {6 Global reference is a kernel side type for all references together } *)
-type global_reference =
+type global_reference = Names.global_reference =
   | VarRef of variable           (** A reference to the section-context. *)
   | ConstRef of Constant.t       (** A reference to the environment. *)
   | IndRef of inductive          (** A reference to an inductive type. *)