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.

2 files changed, 26 insertions, 7 deletions

diff --git a/test-suite/bugs/opened/1596.v b/test-suite/bugs/opened/1596.v
index 91cd09910..7c5dc4167 100644
--- a/test-suite/bugs/opened/1596.v
+++ b/test-suite/bugs/opened/1596.v
@@ -1,10 +1,11 @@
-
 Require Import Relations.
 Require Import FSets.
 Require Import Arith.
 Require Import Omega.
 Unset Standard Proposition Elimination Names.
 
+Set Keyed Unification.
+
 Lemma Bool_elim_bool : forall (b:bool),b=true \/ b=false.
   destruct b;try tauto.
 Qed.
@@ -255,9 +256,6 @@ n).
     induction m;simpl;intro.
     elim (Bool_elim_bool (H.mem (MessageSpi.MNam n,n0) h));intros.
     apply SynInc;apply H.mem_2;trivial.
-    
-    Fail rewrite H in H0. (* !! impossible here !! *)
-Abort.
-(*    discriminate H0.
-  Qed.*)
+    rewrite H in H0. discriminate. (* !! impossible here !! *)
+  Qed.
 End B.
\ No newline at end of file
diff --git a/test-suite/success/keyedrewrite.v b/test-suite/success/keyedrewrite.v
index 438613b44..c99b16e2b 100644
--- a/test-suite/success/keyedrewrite.v
+++ b/test-suite/success/keyedrewrite.v
@@ -1 +1,22 @@
-Lemma foo : 
\ No newline at end of file
+Section foo.
+Variable f : nat -> nat. 
+
+Definition g := f.
+
+Variable lem : g 0 = 0.
+
+Goal f 0 = 0.
+Proof.
+  Fail rewrite lem.
+Abort.
+
+Declare Equivalent Keys @g @f.
+(** Now f and g are considered equivalent heads for subterm selection *)
+Goal f 0 = 0.
+Proof.
+  rewrite lem.
+  reflexivity.
+Qed.
+
+Print Equivalent Keys.
+End foo.