1 files changed, 119 insertions, 35 deletions
diff --git a/theories/Init/Tactics.v b/theories/Init/Tactics.v
index ba210dd6..afe8297e 100644
--- a/theories/Init/Tactics.v
+++ b/theories/Init/Tactics.v
@@ -6,59 +6,143 @@
 (*         *       GNU Lesser General Public License Version 2.1        *)
 (************************************************************************)
 
-(*i $Id: Tactics.v 9268 2006-10-24 12:56:16Z herbelin $ i*)
+(*i $Id: Tactics.v 11072 2008-06-08 16:13:37Z herbelin $ i*)
 
 Require Import Notations.
 Require Import Logic.
 
-(** Useful tactics *)
+(** * Useful tactics *)
+
+(** A tactic for proof by contradiction. With contradict H, 
+    -   H:~A |-  B    gives       |-  A
+    -   H:~A |- ~B    gives  H: B |-  A
+    -   H: A |-  B    gives       |- ~A
+    -   H: A |- ~B    gives  H: B |- ~A
+    -   H:False leads to a resolved subgoal.
+   Moreover, negations may be in unfolded forms, 
+   and A or B may live in Type *)
+
+Ltac contradict H :=
+  let save tac H := let x:=fresh in intro x; tac H; rename x into H
+  in 
+  let negpos H := case H; clear H 
+  in 
+  let negneg H := save negpos H
+  in
+  let pospos H := 
+    let A := type of H in (elimtype False; revert H; try fold (~A))
+  in
+  let posneg H := save pospos H
+  in 
+  let neg H := match goal with 
+   | |- (~_) => negneg H
+   | |- (_->False) => negneg H
+   | |- _ => negpos H
+  end in 
+  let pos H := match goal with 
+   | |- (~_) => posneg H
+   | |- (_->False) => posneg H
+   | |- _ => pospos H
+  end in
+  match type of H with 
+   | (~_) => neg H
+   | (_->False) => neg H
+   | _ => (elim H;fail) || pos H
+  end.
 
-(* A shorter name for generalize + clear, can be seen as an anti-intro *)
+(* Transforming a negative goal [ H:~A |- ~B ] into a positive one [ B |- A ]*)
 
-Tactic Notation "revert" ne_hyp_list(l) := generalize l; clear l.
+Ltac swap H := 
+  idtac "swap is OBSOLETE: use contradict instead.";
+  intro; apply H; clear H.
 
-(* to contradict an hypothesis without copying its type. *)
+(* To contradict an hypothesis without copying its type. *)
 
-Ltac absurd_hyp h := 
-  let T := type of h in 
+Ltac absurd_hyp H := 
+  idtac "absurd_hyp is OBSOLETE: use contradict instead.";
+  let T := type of H in 
   absurd T.
 
-(* Transforming a negative goal [ H:~A |- ~B ] into a positive one [ B |- A ]*)
+(* A useful complement to contradict. Here H:A while G allows to conclude ~A *)
 
-Ltac swap H := intro; apply H; clear H.
+Ltac false_hyp H G := 
+  let T := type of H in absurd T; [ apply G | assumption ].
 
 (* A case with no loss of information. *)
 
 Ltac case_eq x := generalize (refl_equal x); pattern x at -1; case x.
 
-(* A tactic for easing the use of lemmas f_equal, f_equal2, ... *)
-
-Ltac f_equal := 
-  let cg := try congruence in
-  let r := try reflexivity in 
-  match goal with 
-   | |- ?f ?a = ?f' ?a' => cut (a=a'); [cg|r]
-   | |- ?f ?a ?b = ?f' ?a' ?b' => 
-      cut (b=b');[cut (a=a');[cg|r]|r]
-   | |- ?f ?a ?b ?c = ?f' ?a' ?b' ?c'=> 
-      cut (c=c');[cut (b=b');[cut (a=a');[cg|r]|r]|r]
-   | |- ?f ?a ?b ?c ?d= ?f' ?a' ?b' ?c' ?d'=> 
-      cut (d=d');[cut (c=c');[cut (b=b');[cut (a=a');[cg|r]|r]|r]|r]
-  | |- ?f ?a ?b ?c ?d ?e= ?f' ?a' ?b' ?c' ?d' ?e'=> 
-      cut (e=e');[cut (d=d');[cut (c=c');[cut (b=b');[cut (a=a');[cg|r]|r]|r]|r]|r]
-   | _ => idtac
-  end.
-
 (* Rewriting in all hypothesis several times everywhere *)
 
 Tactic Notation "rewrite_all" constr(eq) := repeat rewrite eq in *.
 Tactic Notation "rewrite_all" "<-" constr(eq) := repeat rewrite <- eq in *.
 
-(* Keeping a copy of an expression *)
-
-Ltac remembertac x a :=
-  let x := fresh x in
-  let H := fresh "Heq" x in
-  (set (x:=a) in *; assert (H: x=a) by reflexivity; clearbody x).
-
-Tactic Notation "remember" constr(c) "as" ident(x) := remembertac x c.
+(** Tactics for applying equivalences.
+
+The following code provides tactics "apply -> t", "apply <- t",
+"apply -> t in H" and "apply <- t in H". Here t is a term whose type
+consists of nested dependent and nondependent products with an
+equivalence A <-> B as the conclusion. The tactics with "->" in their
+names apply A -> B while those with "<-" in the name apply B -> A. *)
+
+(* The idea of the tactics is to first provide a term in the context
+whose type is the implication (in one of the directions), and then
+apply it. The first idea is to produce a statement "forall ..., A ->
+B" (call this type T) and then do "assert (H : T)" for a fresh H.
+Thus, T can be proved from the original equivalence and then used to
+perform the application. However, currently in Ltac it is difficult
+to produce such T from the original formula.
+
+Therefore, we first pose the original equivalence as H. If the type of
+H is a dependent product, we create an existential variable and apply
+H to this variable. If the type of H has the form C -> D, then we do a
+cut on C. Once we eliminate all products, we split (i.e., destruct)
+the conjunction into two parts and apply the relevant one. *)
+
+Ltac find_equiv H :=
+let T := type of H in
+lazymatch T with
+| ?A -> ?B =>
+  let H1 := fresh in
+  let H2 := fresh in
+  cut A;
+  [intro H1; pose proof (H H1) as H2; clear H H1;
+   rename H2 into H; find_equiv H |
+   clear H]
+| forall x : ?t, _ =>
+  let a := fresh "a" with
+      H1 := fresh "H" in
+    evar (a : t); pose proof (H a) as H1; unfold a in H1;
+    clear a; clear H; rename H1 into H; find_equiv H
+| ?A <-> ?B => idtac
+| _ => fail "The given statement does not seem to end with an equivalence"
+end.
+
+Ltac bapply lemma todo :=
+let H := fresh in
+  pose proof lemma as H;
+  find_equiv H; [todo H; clear H | .. ].
+
+Tactic Notation "apply" "->" constr(lemma) :=
+bapply lemma ltac:(fun H => destruct H as [H _]; apply H).
+
+Tactic Notation "apply" "<-" constr(lemma) :=
+bapply lemma ltac:(fun H => destruct H as [_ H]; apply H).
+
+Tactic Notation "apply" "->" constr(lemma) "in" ident(J) :=
+bapply lemma ltac:(fun H => destruct H as [H _]; apply H in J).
+
+Tactic Notation "apply" "<-" constr(lemma) "in" ident(J) :=
+bapply lemma ltac:(fun H => destruct H as [_ H]; apply H in J).
+
+(** A tactic simpler than auto that is useful for ending proofs "in one step" *)
+Tactic Notation "now" tactic(t) :=
+t;
+match goal with
+| H : _ |- _ => solve [inversion H]
+| _ => solve [trivial | reflexivity | symmetry; trivial | discriminate | split]
+| _ => fail 1 "Cannot solve this goal"
+end.
+
+(** A tactic to document or check what is proved at some point of a script *)
+Ltac now_show c := change c.