Keyed unification option, compiling the whole standard library

(but deactivated still).

Set Keyed Unification to activate the option, which changes
subterm selection to _always_ use full conversion _after_ finding a
subterm whose head/key matches the key of the term we're looking for.
This applies to rewrite and higher-order unification in
apply/elim/destruct.

Most proof scripts already abide by these semantics. For those that
don't, it's usually only a matter of using:

Declare Equivalent Keys f g.

This make keyed unification consider f and g to match as keys.
This takes care of most cases of abbreviations: typically Def foo :=
bar and rewriting with a bar-headed lhs in a goal mentioning foo works
once they're set equivalent.
For canonical structures, these hints should be automatically declared.

For non-global-reference headed terms, the key is the constructor name
(Sort, Prod...). Evars and metas are no keys.

INCOMPATIBILITIES:
In FMapFullAVL, a Function definition doesn't go through with keyed
unification on.

1 files changed, 2 insertions, 0 deletions

diff --git a/theories/MSets/MSetGenTree.v b/theories/MSets/MSetGenTree.v
index 901574235..d1d9897fb 100644
--- a/theories/MSets/MSetGenTree.v
+++ b/theories/MSets/MSetGenTree.v
@@ -970,6 +970,8 @@ Definition lt (s1 s2 : tree) : Prop :=
  exists s1' s2', Ok s1' /\ Ok s2' /\ eq s1 s1' /\ eq s2 s2'
    /\ L.lt (elements s1') (elements s2').
 
+Declare Equivalent Keys L.eq equivlistA.
+
 Instance lt_strorder : StrictOrder lt.
 Proof.
  split.