Giving a more natural semantics to injection by default.

There were three versions of injection:

1. "injection term" without "as" clause:
   was leaving hypotheses on the goal in reverse order
2. "injection term as ipat", first version:
   was introduction hypotheses using ipat in reverse order without
   checking that the number of ipat was the size of the injection
   (activated with "Unset Injection L2R Pattern Order")
3. "injection term as ipat", second version:
   was introduction hypotheses using ipat in left-to-right order
   checking that the number of ipat was the size of the injection
   and clearing the injecting term by default if an hypothesis
   (activated with "Set Injection L2R Pattern Order", default one from 8.5)

There is now:

4. "injection term" without "as" clause, new version:
   introducing the components of the injection in the context in
   left-to-right order using default intro-patterns "?"
   and clearing the injecting term by default if an hypothesis
   (activated with "Set Structural Injection")

The new versions 3. and 4. are the "expected" ones in the sense that
they have the following good properties:
- introduction in the context is in the natural left-to-right order
- "injection" behaves the same with and without "as", always
  introducing the hypotheses in the goal what corresponds to the
  natural expectation as the changes I made in the proof scripts for
  adaptation confirm
- clear the "injection" hypothesis when an hypothesis which is the
  natural expectation as the changes I made in the proof scripts for
  adaptation confirm

The compatibility can be preserved by "Unset Structural Injection" or
by calling "simple injection".

The flag is currently off.

1 files changed, 6 insertions, 8 deletions

diff --git a/theories/Lists/List.v b/theories/Lists/List.v
index b66699220..9886ae6a8 100644
--- a/theories/Lists/List.v
+++ b/theories/Lists/List.v
@@ -248,8 +248,7 @@ Section Facts.
     generalize (app_nil_r l); intros E.
     rewrite -> E; auto.
     intros.
-    injection H.
-    intro.
+    injection H as H H0.
     assert ([] = l ++ a0 :: l0) by auto.
     apply app_cons_not_nil in H1 as [].
   Qed.
@@ -335,7 +334,7 @@ Section Facts.
     absurd (length (x1 :: l1 ++ l) <= length l).
     simpl; rewrite app_length; auto with arith.
     rewrite H; auto with arith.
-    injection H; clear H; intros; f_equal; eauto.
+    injection H as H H0; f_equal; eauto.
   Qed.
 
 End Facts.
@@ -518,7 +517,7 @@ Section Elts.
   Proof.
     revert l.
     induction n as [|n IH]; intros [|x l] H; simpl in *; try easy.
-    - exists nil; exists l. injection H; clear H; intros; now subst.
+    - exists nil; exists l. now injection H as ->.
     - destruct (IH _ H) as (l1 & l2 & H1 & H2).
       exists (x::l1); exists l2; simpl; split; now f_equal.
   Qed.
@@ -1385,9 +1384,8 @@ End Fold_Right_Recursor.
     Lemma combine_split : forall (l:list A)(l':list B), length l = length l' ->
       split (combine l l') = (l,l').
     Proof.
-      induction l; destruct l'; simpl; intros; auto; try discriminate.
-      injection H; clear H; intros.
-      rewrite IHl; auto.
+      induction l, l'; simpl; trivial; try discriminate.
+      now intros [= ->%IHl].
     Qed.
 
     Lemma in_combine_l : forall (l:list A)(l':list B)(x:A)(y:B),
@@ -1471,7 +1469,7 @@ End Fold_Right_Recursor.
       destruct (in_app_or _ _ _ H); clear H.
       destruct (in_map_iff (fun y : B => (a, y)) l' (x,y)) as (H1,_).
       destruct (H1 H0) as (z,(H2,H3)); clear H0 H1.
-      injection H2; clear H2; intros; subst; intuition.
+      injection H2 as -> ->; intuition.
       intuition.
     Qed.