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/test-suite/coqchk/cumulativity.v b/test-suite/coqchk/cumulativity.v
index d63a3548e..5f4500715 100644
--- a/test-suite/coqchk/cumulativity.v
+++ b/test-suite/coqchk/cumulativity.v
@@ -25,7 +25,7 @@ Section ListLower.
 
 End ListLower.
 
-Lemma LowerL_Lem@{i j} (A : Type@{j}) (l : List@{i} A) : l = LowerL l.
+Lemma LowerL_Lem@{i j|j<i+} (A : Type@{j}) (l : List@{i} A) : l = LowerL l.
 Proof. reflexivity. Qed.
 (*
 I disable these tests because cqochk can't process them when compiled with