Library FSetWeakNotin

Lemmas and tactics for working with and solving goals related to non-membership in finite sets. The main tactic of interest here is solve_notin.

Implicit arguments are declared by default in this library.

Require Import Coq.FSets.FSetInterface.

Require Import CoqFSetDecide.

Implementation

Module Notin_fun
(E : DecidableType) (Import X : FSetInterface.WSfun E).

Module Import D := CoqFSetDecide.WDecide_fun E X.

Facts about set non-membership

Section Lemmas.

Variables x y : elt.
Variable s s' : X.t.

Lemma notin_empty_1 :
  ~ In x empty.

Lemma notin_add_1 :
  ~ In y (add x s) ->
  ~ E.eq x y.

Lemma notin_add_1' :
  ~ In y (add x s) ->
  x <> y.

Lemma notin_add_2 :
  ~ In y (add x s) ->
  ~ In y s.

Lemma notin_add_3 :
  ~ E.eq x y ->
  ~ In y s ->
  ~ In y (add x s).

Lemma notin_singleton_1 :
  ~ In y (singleton x) ->
  ~ E.eq x y.

Lemma notin_singleton_1' :
  ~ In y (singleton x) ->
  x <> y.

Lemma notin_singleton_2 :
  ~ E.eq x y ->
  ~ In y (singleton x).

Lemma notin_remove_1 :
  ~ In y (remove x s) ->
  E.eq x y \/ ~ In y s.

Lemma notin_remove_2 :
  ~ In y s ->
  ~ In y (remove x s).

Lemma notin_remove_3 :
  E.eq x y ->
  ~ In y (remove x s).

Lemma notin_remove_3' :
  x = y ->
  ~ In y (remove x s).

Lemma notin_union_1 :
  ~ In x (union s s') ->
  ~ In x s.

Lemma notin_union_2 :
  ~ In x (union s s') ->
  ~ In x s'.

Lemma notin_union_3 :
  ~ In x s ->
  ~ In x s' ->
  ~ In x (union s s').

Lemma notin_inter_1 :
  ~ In x (inter s s') ->
  ~ In x s \/ ~ In x s'.

Lemma notin_inter_2 :
  ~ In x s ->
  ~ In x (inter s s').

Lemma notin_inter_3 :
  ~ In x s' ->
  ~ In x (inter s s').

Lemma notin_diff_1 :
  ~ In x (diff s s') ->
  ~ In x s \/ In x s'.

Lemma notin_diff_2 :
  ~ In x s ->
  ~ In x (diff s s').

Lemma notin_diff_3 :
  In x s' ->
  ~ In x (diff s s').

End Lemmas.

Hints

Hint Resolve
  @notin_empty_1 @notin_add_3 @notin_singleton_2 @notin_remove_2
  @notin_remove_3 @notin_remove_3' @notin_union_3 @notin_inter_2
  @notin_inter_3 @notin_diff_2 @notin_diff_3.

Tactics for non-membership

destruct_notin decomposes all hypotheses of the form ~ In x s.

Ltac destruct_notin :=
  match goal with
    | H : In ?x ?s -> False |- _ =>
      change (~ In x s) in H;
      destruct_notin
    | |- In ?x ?s -> False =>
      change (~ In x s);
      destruct_notin
    | H : ~ In _ empty |- _ =>
      clear H;
      destruct_notin
    | H : ~ In ?y (add ?x ?s) |- _ =>
      let J1 := fresh "NotInTac" in
      let J2 := fresh "NotInTac" in
      pose proof H as J1;
      pose proof H as J2;
      apply notin_add_1 in H;
      apply notin_add_1' in J1;
      apply notin_add_2 in J2;
      destruct_notin
    | H : ~ In ?y (singleton ?x) |- _ =>
      let J := fresh "NotInTac" in
      pose proof H as J;
      apply notin_singleton_1 in H;
      apply notin_singleton_1' in J;
      destruct_notin
    | H : ~ In ?y (remove ?x ?s) |- _ =>
      let J := fresh "NotInTac" in
      apply notin_remove_1 in H;
      destruct H as [J | J];
      destruct_notin
    | H : ~ In ?x (union ?s ?s') |- _ =>
      let J := fresh "NotInTac" in
      pose proof H as J;
      apply notin_union_1 in H;
      apply notin_union_2 in J;
      destruct_notin
    | H : ~ In ?x (inter ?s ?s') |- _ =>
      let J := fresh "NotInTac" in
      apply notin_inter_1 in H;
      destruct H as [J | J];
      destruct_notin
    | H : ~ In ?x (diff ?s ?s') |- _ =>
      let J := fresh "NotInTac" in
      apply notin_diff_1 in H;
      destruct H as [J | J];
      destruct_notin
    | _ =>
      idtac
  end.

solve_notin decomposes hypotheses of the form ~ In x s and then tries some simple heuristics for solving the resulting goals.

Ltac solve_notin :=
  intros;
  destruct_notin;
  repeat first [ apply notin_union_3
               | apply notin_add_3
               | apply notin_singleton_2
               | apply notin_empty_1
               ];
  auto;
  try tauto;
  fail "Not solvable by [solve_notin]; try [destruct_notin]".

Examples and test cases

These examples and test cases are not meant to be exhaustive.

Lemma test_solve_notin_1 : forall x E F G,
  ~ In x (union E F) ->
  ~ In x G ->
  ~ In x (union E G).

Lemma test_solve_notin_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).

Lemma test_solve_notin_3 : forall x y,
  ~ E.eq x y ->
  ~ In x (singleton y) /\ ~ In y (singleton x).

Lemma test_solve_notin_4 : forall x y E F G,
  ~ In x (union E (union (singleton x) F)) ->
  ~ In y G.

Lemma test_solve_notin_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.

Lemma test_solve_notin_6 : forall x y E,
  ~ In x (add y E) ->
  ~ E.eq x y /\ ~ In x E.

Lemma test_solve_notin_7 : forall x,
  ~ In x (singleton x) ->
  False.

End Notin_fun.

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