Module MSetLogicalFacts.
Export Decidable.
Export Setoid.
(** ** Lemmas and Tactics About Decidable Propositions *)
(** ** Propositional Equivalences Involving Negation These are all written with the unfolded form of negation, since I am not sure if setoid rewriting will always perform conversion. *)
(** ** Tactics for Negations *)
Tactic Notation "fold" "any" "not" :=
repeat (
match goal with
| H: context [?P -> False] |- _ =>
fold (~ P) in H
| |- context [?P -> False] =>
fold (~ P)
end).
(** [push not using db] will pushes all negations to the leaves of propositions in the goal, using the lemmas in [db] to assist in checking the decidability of the propositions involved.  If [using db] is omitted, then [core] will be used.  Additional versions are provided to manipulate the hypotheses or the hypotheses and goal together.  XXX: This tactic and the similar subsequent ones should have been defined using [autorewrite]. However, dealing with multiples rewrite sites and side-conditions is done more cleverly with the following explicit analysis of goals. *)
Ltac or_not_l_iff P Q tac :=
(rewrite (or_not_l_iff_1 P Q) by tac) ||
(rewrite (or_not_l_iff_2 P Q) by tac).
Ltac or_not_r_iff P Q tac :=
(rewrite (or_not_r_iff_1 P Q) by tac) ||
(rewrite (or_not_r_iff_2 P Q) by tac).
Ltac or_not_l_iff_in P Q H tac :=
(rewrite (or_not_l_iff_1 P Q) in H by tac) ||
(rewrite (or_not_l_iff_2 P Q) in H by tac).
Ltac or_not_r_iff_in P Q H tac :=
(rewrite (or_not_r_iff_1 P Q) in H by tac) ||
(rewrite (or_not_r_iff_2 P Q) in H by tac).
Tactic Notation "push" "not" "using" ident(db) :=
let dec := solve_decidable using db in
unfold not, iff;
repeat (
match goal with
| |- context [True -> False] => rewrite not_true_iff
| |- context [False -> False] => rewrite not_false_iff
| |- context [(?P -> False) -> False] => rewrite (not_not_iff P) by dec
| |- context [(?P -> False) -> (?Q -> False)] =>
rewrite (contrapositive P Q) by dec
| |- context [(?P -> False) \/ ?Q] => or_not_l_iff P Q dec
| |- context [?P \/ (?Q -> False)] => or_not_r_iff P Q dec
| |- context [(?P -> False) -> ?Q] => rewrite (imp_not_l P Q) by dec
| |- context [?P \/ ?Q -> False] => rewrite (not_or_iff P Q)
| |- context [?P /\ ?Q -> False] => rewrite (not_and_iff P Q)
| |- context [(?P -> ?Q) -> False] => rewrite (not_imp_iff P Q) by dec
end);
fold any not.
Tactic Notation "push" "not" :=
push not using core.
Tactic Notation
"push" "not" "in" "*" "|-" "using" ident(db) :=
let dec := solve_decidable using db in
unfold not, iff in * |-;
repeat (
match goal with
| H: context [True -> False] |- _ => rewrite not_true_iff in H
| H: context [False -> False] |- _ => rewrite not_false_iff in H
| H: context [(?P -> False) -> False] |- _ =>
rewrite (not_not_iff P) in H by dec
| H: context [(?P -> False) -> (?Q -> False)] |- _ =>
rewrite (contrapositive P Q) in H by dec
| H: context [(?P -> False) \/ ?Q] |- _ => or_not_l_iff_in P Q H dec
| H: context [?P \/ (?Q -> False)] |- _ => or_not_r_iff_in P Q H dec
| H: context [(?P -> False) -> ?Q] |- _ =>
rewrite (imp_not_l P Q) in H by dec
| H: context [?P \/ ?Q -> False] |- _ => rewrite (not_or_iff P Q) in H
| H: context [?P /\ ?Q -> False] |- _ => rewrite (not_and_iff P Q) in H
| H: context [(?P -> ?Q) -> False] |- _ =>
rewrite (not_imp_iff P Q) in H by dec
end);
fold any not.
Tactic Notation "push" "not" "in" "*" "|-"  :=
push not in * |- using core.
Tactic Notation "push" "not" "in" "*" "using" ident(db) :=
push not using db; push not in * |- using db.
Tactic Notation "push" "not" "in" "*" :=
push not in * using core.

(** A simple test case to see how this works.  *)
Lemma test_push : forall P Q R : Prop,
decidable P ->
decidable Q ->
(~ True) ->
(~ False) ->
(~ ~ P) ->
(~ (P /\ Q) -> ~ R) ->
((P /\ Q) \/ ~ R) ->
(~ (P /\ Q) \/ R) ->
(R \/ ~ (P /\ Q)) ->
(~ R \/ (P /\ Q)) ->
(~ P -> R) ->
(~ ((R -> P) \/ (Q -> R))) ->
(~ (P /\ R)) ->
(~ (P -> R)) ->
True.