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/FSets/FSetCompat.v b/theories/FSets/FSetCompat.v
index 6b3d86d39..b1769da3d 100644
--- a/theories/FSets/FSetCompat.v
+++ b/theories/FSets/FSetCompat.v
@@ -283,6 +283,8 @@ Module Update_WSets
 
   Lemma is_empty_spec : is_empty s = true <-> Empty s.
   Proof. intros; symmetry; apply MF.is_empty_iff. Qed.
+  
+  Declare Equivalent Keys In M.In.
 
   Lemma add_spec : In y (add x s) <-> E.eq y x \/ In y s.
   Proof. intros. rewrite MF.add_iff. intuition. Qed.