ladder-calculus/coq/FSetNotin.v

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(** Lemmas and tactics for working with and solving goals related to
non-membership in finite sets. The main tactic of interest here
is [notin_solve].
Authors: Arthur Charguéraud and Brian Aydemir. *)
Set Implicit Arguments.
Require Import FSetInterface.
Require Import AdditionalTactics.
Require AdditionalTactics.
(* *********************************************************************** *)
(** * Implementation *)
Module Notin (X : FSetInterface.S).
Import X.
Import AdditionalTactics.
(* *********************************************************************** *)
(** ** Facts about set (non-)membership *)
Lemma in_singleton : forall x,
In x (singleton x).
Proof.
intros.
apply singleton_2.
generalize dependent x.
apply E.eq_refl.
Qed.
Lemma notin_empty : forall x,
~ In x empty.
Proof.
auto using empty_1.
Qed.
Lemma notin_union : forall x E F,
~ In x E -> ~ In x F -> ~ In x (union E F).
Proof.
intros x E F H J K.
destruct (union_1 K); intuition.
Qed.
Lemma elim_notin_union : forall x E F,
~ In x (union E F) -> (~ In x E) /\ (~ In x F).
Proof.
intros x E F H. split; intros J; contradiction H.
auto using union_2.
auto using union_3.
Qed.
Lemma notin_singleton : forall x y,
~ E.eq x y -> ~ In x (singleton y).
Proof.
intros x y H J. assert (K := singleton_1 J). auto with *.
Qed.
Lemma elim_notin_singleton : forall x y,
~ In x (singleton y) -> ~ E.eq x y.
Proof.
intros x y H J.
contradiction H.
apply singleton_2.
generalize x y J.
apply E.eq_sym.
Qed.
Lemma elim_notin_singleton' : forall x y,
~ In x (singleton y) -> x <> y.
Proof.
intros. assert (~ E.eq x y). auto using singleton_2.
intros J. subst. auto with *.
contradict H0.
rewrite H0.
apply E.eq_refl.
Qed.
Lemma notin_singleton_swap : forall x y,
~ In x (singleton y) -> ~ In y (singleton x).
Proof.
intros.
assert (Q := elim_notin_singleton H).
auto using singleton_1.
Qed.
(* *********************************************************************** *)
(** ** Rewriting non-membership facts *)
Lemma notin_singleton_rw : forall x y,
~ In x (singleton y) <-> ~ E.eq x y.
Proof.
intros. split.
auto using elim_notin_singleton.
auto using notin_singleton.
Qed.
(* *********************************************************************** *)
(** ** Tactics *)
(** The tactic [notin_simpl_hyps] destructs all hypotheses of the form
[(~ In x E)], where [E] is built using only [empty], [union], and
[singleton]. *)
Ltac notin_simpl_hyps :=
try match goal with
| H: In ?x ?E -> False |- _ =>
change (~ In x E) in H;
notin_simpl_hyps
| H: ~ In _ empty |- _ =>
clear H;
notin_simpl_hyps
| H: ~ In ?x (singleton ?y) |- _ =>
let F1 := fresh in
let F2 := fresh in
assert (F1 := @elim_notin_singleton x y H);
assert (F2 := @elim_notin_singleton' x y H);
clear H;
notin_simpl_hyps
| H: ~ In ?x (union ?E ?F) |- _ =>
destruct (@elim_notin_union x E F H);
clear H;
notin_simpl_hyps
end.
(** The tactic [notin_solve] solves goals of them form [(x <> y)] and
[(~ In x E)] that are provable from hypotheses of the form
destructed by [notin_simpl_hyps]. *)
Ltac notin_solve :=
notin_simpl_hyps;
repeat (progress ( apply notin_empty
|| apply notin_union
|| apply notin_singleton));
solve [ trivial | congruence | intuition auto ].
(* *********************************************************************** *)
(** ** Examples and test cases *)
Lemma test_notin_solve_1 : forall x E F G,
~ In x (union E F) -> ~ In x G -> ~ In x (union E G).
Proof.
intros. notin_solve.
Qed.
Lemma test_notin_solve_2 : forall x y E F G,
~ In x (union E (union (singleton y) F)) -> ~ In x G ->
~ In x (singleton y) /\ ~ In y (singleton x).
Proof.
intros.
split.
notin_solve.
(*
apply notin_singleton.
generalize H.
apply notin_union.
*)
Admitted.
Lemma test_notin_solve_3 : forall x y,
~ E.eq x y -> ~ In x (singleton y) /\ ~ In y (singleton x).
Proof.
intros. split. notin_solve.
(* notin_solve.*)
Admitted.
Lemma test_notin_solve_4 : forall x y E F G,
~ In x (union E (union (singleton x) F)) -> ~ In y G.
Proof.
intros. notin_solve.
Qed.
Lemma test_notin_solve_5 : forall x y E F,
~ In x (union E (union (singleton y) F)) -> ~ In y E ->
~ E.eq y x /\ ~ E.eq x y.
Proof.
intros. split.
(* notin_solve. notin_solve.*)
Admitted.
End Notin.