881 lines
31 KiB
Coq
881 lines
31 KiB
Coq
Require Import Nat.
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Require Import PeanoNat.
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Require Import List.
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Import ListNotations.
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(** * Various definitions
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Different definitions of a subsequence are given; they are proved
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below to be equivalent, allowing to choose the most convenient at
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any step of a proof.
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*)
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Definition subsequence {X: Type} (l s : list X) :=
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exists (l1: list X) (l2 : list (list X)),
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length s = length l2
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/\ l = l1 ++ flat_map (fun e => (fst e) :: (snd e)) (combine s l2).
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Definition subsequence2 {X: Type} (l s : list X) :=
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exists (t: list bool),
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length t = length l /\ s = map snd (filter fst (combine t l)).
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Fixpoint subsequence3 {X: Type} (l s : list X) : Prop :=
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match s with
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| nil => True
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| hd::tl => exists l1 l2, l = l1 ++ (hd::l2) /\ subsequence3 l2 tl
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end.
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(** * Elementary properties
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*)
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Theorem subsequence_nil_r {X: Type}: forall (l : list X), subsequence l nil.
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Proof.
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intro l. exists l. exists nil. rewrite app_nil_r. split; easy.
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Qed.
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Theorem subsequence2_nil_r {X: Type} : forall (l : list X), subsequence2 l nil.
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Proof.
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intro l.
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exists (repeat false (length l)). rewrite repeat_length.
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split; try induction l; easy.
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Qed.
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Theorem subsequence3_nil_r {X: Type} : forall (l : list X), subsequence3 l nil.
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Proof.
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intro l. reflexivity.
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Qed.
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Theorem subsequence_nil_cons_r {X: Type}: forall (l: list X) (a:X),
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~ subsequence nil (a::l).
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Proof.
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intros l a. intro H.
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destruct H. destruct H. destruct H.
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destruct x. rewrite app_nil_l in H0.
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destruct x0. apply PeanoNat.Nat.neq_succ_0 in H. contradiction H.
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apply nil_cons in H0. contradiction H0.
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apply nil_cons in H0. contradiction H0.
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Qed.
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Theorem subsequence2_nil_cons_r {X: Type}: forall (l: list X) (a:X),
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~ subsequence2 nil (a::l).
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Proof.
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intros l a. intro H. destruct H.
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destruct H. assert (x = nil). destruct x. reflexivity.
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apply PeanoNat.Nat.neq_succ_0 in H. contradiction H.
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rewrite H1 in H0. symmetry in H0. apply nil_cons in H0. contradiction H0.
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Qed.
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Theorem subsequence3_nil_cons_r {X: Type}: forall (l: list X) (a:X),
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~ subsequence3 nil (a::l).
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Proof.
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intros l a. intro H. destruct H. destruct H. destruct H.
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destruct x; apply nil_cons in H; contradiction H.
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Qed.
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Theorem subsequence_cons_l {X: Type}: forall (l s: list X) (a: X),
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subsequence l s -> subsequence (a::l) s.
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Proof.
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intros l s a. intro H. destruct H. destruct H. destruct H.
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exists (a::x). exists x0. split. assumption. rewrite H0. reflexivity.
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Qed.
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Theorem subsequence2_cons_l {X: Type} : forall (l s: list X) (a: X),
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subsequence2 l s -> subsequence2 (a::l) s.
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Proof.
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intros l s a. intro H. destruct H. destruct H. exists (false::x).
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split; try apply eq_S; assumption.
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Qed.
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Theorem subsequence3_cons_l {X: Type} : forall (l s: list X) (a: X),
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subsequence3 l s -> subsequence3 (a::l) s.
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Proof.
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intros l s a. intro H. destruct s. apply subsequence3_nil_r.
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destruct H. destruct H. destruct H. exists (a::x0). exists x1. rewrite H.
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split; easy.
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Qed.
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Theorem subsequence_cons_r {X: Type} : forall (l s: list X) (a: X),
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subsequence l (a::s) -> subsequence l s.
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Proof.
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intros l s a. intro H. destruct H. destruct H. destruct H.
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destruct x0. apply PeanoNat.Nat.neq_succ_0 in H. contradiction H.
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exists (x++a::l0). exists x0. split. inversion H. reflexivity. rewrite H0.
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rewrite <- app_assoc. apply app_inv_head_iff. reflexivity.
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Qed.
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Theorem subsequence2_cons_r {X: Type} : forall (l s: list X) (a: X),
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subsequence2 l (a::s) -> subsequence2 l s.
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Proof.
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intro l. induction l. intros. apply subsequence2_nil_cons_r in H.
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contradiction H. intros s a0 . intro H. destruct H. destruct H. destruct x.
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symmetry in H0. apply nil_cons in H0. contradiction H0.
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destruct b. simpl in H0. inversion H0.
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exists (false::x). split; try rewrite <- H; reflexivity.
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apply subsequence2_cons_l. apply IHl with (a := a0).
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exists x. split; inversion H; easy.
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Qed.
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Theorem subsequence3_cons_r {X: Type} : forall (l s: list X) (a: X),
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subsequence3 l (a::s) -> subsequence3 l s.
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Proof.
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intros l s a. intro H. simpl in H. destruct H. destruct H.
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destruct s. apply subsequence3_nil_r. destruct H. simpl in H0.
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destruct H0. destruct H0. destruct H0.
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exists (x ++ a::x2). exists x3.
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rewrite H. rewrite H0. split. rewrite <- app_assoc.
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rewrite app_comm_cons. reflexivity. assumption.
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Qed.
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Theorem subsequence_cons_eq {X: Type} : forall (l1 l2: list X) (a: X),
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subsequence (a::l1) (a::l2) <-> subsequence l1 l2.
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Proof.
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intros l s a. split; intro H; destruct H; destruct H; destruct H.
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destruct x. destruct x0.
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apply PeanoNat.Nat.neq_succ_0 in H. contradiction H.
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inversion H0. exists l0. exists x0.
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inversion H. rewrite H3. split; reflexivity.
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destruct x0.
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apply PeanoNat.Nat.neq_succ_0 in H. contradiction H.
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exists (x1 ++ (a::l0)). exists x0. inversion H. rewrite H2.
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split. reflexivity. inversion H0. rewrite <- app_assoc.
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apply app_inv_head_iff. rewrite app_comm_cons. reflexivity.
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exists nil. exists (x::x0). simpl.
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split; [ rewrite H | rewrite H0 ]; reflexivity.
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Qed.
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Theorem subsequence2_cons_eq {X: Type}: forall (l1 l2: list X) (a: X),
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subsequence2 (a::l1) (a::l2) <-> subsequence2 l1 l2.
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Proof.
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intros l s a. split; intro H; destruct H; destruct H.
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destruct x. inversion H0. destruct b. exists (x).
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split; inversion H; try rewrite H2; inversion H0; reflexivity.
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inversion H. assert (subsequence2 l (a::s)).
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exists x. split; assumption.
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apply subsequence2_cons_r with (a := a). assumption.
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exists (true :: x). split. apply eq_S. assumption. rewrite H0. reflexivity.
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Qed.
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Theorem subsequence3_cons_eq {X: Type} : forall (l1 l2: list X) (a: X),
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subsequence3 (a::l1) (a::l2) <-> subsequence3 l1 l2.
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Proof.
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intros l s a. split; intro H.
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destruct H. destruct H. destruct H.
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destruct x. inversion H. assumption.
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destruct s. apply subsequence3_nil_r.
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destruct H0. destruct H0. destruct H0.
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exists (x1 ++ (a::x3)). exists x4.
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inversion H. rewrite H0. rewrite <- app_assoc.
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rewrite app_comm_cons. split; easy.
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exists nil. exists l. split; easy.
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Qed.
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(** * Equivalence of all definitions
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The following three implications are proved:
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- subsequence l s -> subsequence2 l s
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- subsequence2 l s -> subsequence3 l s
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- subsequence3 l s -> subsequence l s
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*)
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Theorem subsequence_eq_def_1 {X: Type} :
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forall l s : list X, subsequence l s -> subsequence2 l s.
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Proof.
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intros l s. intro H. destruct H. destruct H. destruct H.
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exists (
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(repeat false (length x)) ++
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(flat_map (fun e => true :: (repeat false (length e))) x0)).
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split.
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rewrite H0. rewrite app_length. rewrite app_length. rewrite repeat_length.
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rewrite Nat.add_cancel_l. rewrite flat_map_length. rewrite flat_map_length.
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assert (forall v (u: list X),
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length u = length v
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-> map (fun e => length (fst e :: snd e)) (combine u v)
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= map (fun e => length (true :: repeat false (length e))) v).
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intro v. induction v; intro u; intro I.
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apply length_zero_iff_nil in I. rewrite I. reflexivity.
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destruct u. apply O_S in I. contradiction I.
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simpl. rewrite IHv. rewrite repeat_length. reflexivity.
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inversion I. reflexivity.
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rewrite H1; inversion H; reflexivity. rewrite H0.
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assert (forall (u: list X) v w,
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filter fst (combine (repeat false (length u) ++ v) (u ++ w))
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= filter fst (combine v w)).
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intro u. induction u; intros v w. reflexivity. simpl. apply IHu.
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assert (forall (v: list (list X)) (u : list X),
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length u = length v
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-> u = map snd (filter fst (combine
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(flat_map (fun e => true:: repeat false (length e)) v)
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(flat_map (fun e => fst e :: snd e) (combine u v))))).
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intro v. induction v; intro u; intro I.
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apply length_zero_iff_nil in I. rewrite I. reflexivity.
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destruct u. apply O_S in I. contradiction I.
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simpl. rewrite H1. rewrite <- IHv; inversion I; reflexivity.
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rewrite H1. rewrite <- H2; inversion H; reflexivity.
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Qed.
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Theorem subsequence_eq_def_2 {X: Type} :
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forall l s : list X, subsequence2 l s -> subsequence3 l s.
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Proof.
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intros l s. intro H. destruct H. destruct H.
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assert (I: forall u (v w: list X),
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length u = length w
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-> v = map snd (filter fst (combine u w))
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-> subsequence3 w v).
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intro u. induction u; intros v w; intros I J.
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rewrite J. apply subsequence3_nil_r.
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destruct v. apply subsequence3_nil_r.
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destruct w. apply Nat.neq_succ_0 in I. contradiction I.
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destruct a. exists nil. exists w. inversion J.
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apply IHu in H3. split; inversion J; try rewrite <- H5; easy.
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inversion I. reflexivity.
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assert (subsequence3 w (x0::v)). apply IHu; inversion I; easy.
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apply subsequence3_cons_l; assumption.
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apply I with (u := x); assumption.
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Qed.
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Theorem subsequence_eq_def_3 {X: Type} :
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forall l s : list X, subsequence3 l s -> subsequence l s.
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Proof.
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intros l s. generalize l. induction s; intro l0; intro H.
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apply subsequence_nil_r. destruct H. destruct H. destruct H.
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apply IHs in H0. destruct H0. destruct H0. destruct H0.
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exists x. exists (x1:: x2). split. simpl. rewrite H0.
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reflexivity. rewrite H. rewrite H1. reflexivity.
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Qed.
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(** * Decidability of all definitions
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*)
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Theorem subsequence2_dec {X: Type}:
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(forall x y : X, {x = y} + {x <> y})
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-> forall (l s : list X), { subsequence2 l s } + { ~ subsequence2 l s }.
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Proof.
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intro H.
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intro l. induction l; intro s. destruct s. left. apply subsequence2_nil_r.
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right. apply subsequence2_nil_cons_r.
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assert({subsequence2 l s} + {~ subsequence2 l s}). apply IHl. destruct H0.
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rewrite <- subsequence2_cons_eq with (a := a) in s0.
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apply subsequence2_cons_r in s0. left; assumption.
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destruct s. left. apply subsequence2_nil_r.
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assert ({x=a}+{x<>a}). apply H. destruct H0. rewrite e.
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destruct IHl with (s := s); [ left | right ];
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rewrite subsequence2_cons_eq; assumption.
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right. intro I.
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destruct I. destruct H0. destruct x0.
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symmetry in H1. apply nil_cons in H1. contradiction H1.
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destruct b.
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inversion H1. rewrite H3 in n0. easy.
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apply n. exists x0; split; inversion H0; easy.
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Qed.
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Theorem subsequence3_dec {X: Type}:
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(forall x y : X, {x = y} + {x <> y})
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-> forall (l s : list X), { subsequence3 l s } + { ~ subsequence3 l s }.
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Proof.
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intro H. intros l s.
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assert ({ subsequence2 l s } + { ~ subsequence2 l s }).
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apply subsequence2_dec. assumption. destruct H0.
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apply subsequence_eq_def_2 in s0. left. assumption.
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right. intro I.
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apply subsequence_eq_def_3 in I.
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apply subsequence_eq_def_1 in I.
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apply n in I. contradiction I.
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Qed.
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Theorem subsequence_dec {X: Type}:
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(forall x y : X, {x = y} + {x <> y})
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-> forall (l s : list X), { subsequence l s } + { ~ subsequence l s }.
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Proof.
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intro H. intros l s.
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assert ({ subsequence3 l s } + { ~ subsequence3 l s }).
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apply subsequence3_dec. assumption. destruct H0.
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apply subsequence_eq_def_3 in s0. left. assumption.
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right. intro I.
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apply subsequence_eq_def_1 in I.
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apply subsequence_eq_def_2 in I.
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apply n in I. contradiction I.
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Qed.
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(** * Various general properties
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*)
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Theorem subsequence_id {X: Type} :
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forall u : list X, subsequence u u.
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Proof.
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intro u. apply subsequence_eq_def_3.
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induction u. easy. exists nil. exists u.
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split; easy.
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Qed.
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Theorem subsequence_app {X: Type} :
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forall l1 s1 l2 s2 : list X,
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subsequence l1 s1 -> subsequence l2 s2 -> subsequence (l1++l2) (s1++s2).
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Proof.
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intros l1 s1 l2 s2. intros H I.
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apply subsequence_eq_def_3. apply subsequence_eq_def_2.
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apply subsequence_eq_def_1 in H.
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apply subsequence_eq_def_1 in I.
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destruct H. destruct I. exists (x++x0). destruct H. destruct H0.
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split. rewrite app_length. rewrite app_length.
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rewrite H. rewrite H0. reflexivity.
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rewrite H1. rewrite H2.
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assert (J: forall (t : list bool) (u : list X) (v: list bool) (w : list X),
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length t = length u
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-> combine (t++v) (u++w) = (combine t u) ++ (combine v w)).
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intros t u v w. generalize u. induction t; intro u0; intro K.
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replace u0 with (nil : list X). reflexivity.
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destruct u0. reflexivity. apply O_S in K. contradiction K.
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destruct u0. apply PeanoNat.Nat.neq_succ_0 in K. contradiction K.
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simpl. rewrite IHt. reflexivity. inversion K. reflexivity.
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rewrite J. rewrite filter_app. rewrite map_app. reflexivity.
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assumption.
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Qed.
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Theorem subsequence_trans {X: Type} :
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forall (l1 l2 l3: list X),
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subsequence l1 l2 -> subsequence l2 l3 -> subsequence l1 l3.
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Proof.
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intros l1 l2 l3. intros H I.
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apply subsequence_eq_def_3. apply subsequence_eq_def_2.
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apply subsequence_eq_def_1 in I.
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destruct H. destruct H. destruct H. destruct I. destruct H1.
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exists (
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(repeat false (length x)) ++
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(flat_map (fun e => (fst e) :: (repeat false (length (snd e))))
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(combine x1 x0))).
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split.
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rewrite app_length. rewrite repeat_length.
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rewrite H0. rewrite app_length. rewrite Nat.add_cancel_l.
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rewrite flat_map_length. rewrite flat_map_length.
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assert (forall (u: list X) (v: list (list X)),
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length u = length v
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-> list_sum (map (fun z => length (fst z :: snd z))
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(combine u v))
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= list_sum (map (fun z => S (length z)) v)).
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intros u v. generalize u. induction v; intro u0; intro I.
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apply length_zero_iff_nil in I. rewrite I. reflexivity.
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destruct u0. apply O_S in I. contradiction I.
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simpl. rewrite IHv. reflexivity. inversion I. reflexivity.
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rewrite H3.
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assert (forall (u: list bool) (v: list (list X)),
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length u = length v
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-> list_sum (map (fun z => length (fst z :: repeat false (length (snd z))))
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(combine u v))
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= list_sum (map (fun z => S (length z)) v)).
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intros u v. generalize u.
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induction v; intro u0; intro I; destruct u0. reflexivity.
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apply PeanoNat.Nat.neq_succ_0 in I. contradiction I.
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apply O_S in I. contradiction I.
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simpl. rewrite IHv. rewrite repeat_length. reflexivity.
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inversion I. reflexivity. rewrite H4. reflexivity.
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rewrite H1. rewrite H. reflexivity. assumption.
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assert (K: forall (w v: list X) u,
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filter fst (combine ((repeat false (length w)) ++ u)
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(w ++ v)) = filter fst (combine u v)).
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intro w0. induction w0. reflexivity. apply IHw0.
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rewrite H2. rewrite H0.
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assert (forall (u v: list X) (w: list bool),
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map snd (filter fst (combine ((repeat false (length u)) ++ w) (u ++ v)))
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= map snd (filter fst (combine w v))).
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intro u. induction u; intros v w. reflexivity.
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apply IHu. rewrite H3.
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assert (forall (u: list bool) (v: list X) (w: list (list X)),
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length u = length w
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-> length u = length v
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-> filter fst (combine
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(flat_map
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(fun e => fst e:: (repeat false (length (snd e))))
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(combine u w))
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(flat_map (fun e => fst e :: snd e) (combine v w)))
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= filter fst (combine u v)).
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intros u v w. generalize u. generalize v.
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induction w; intros v0 u0; intros I J.
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apply length_zero_iff_nil in I. rewrite I. reflexivity.
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destruct u0. reflexivity. destruct v0.
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apply PeanoNat.Nat.neq_succ_0 in J; contradiction J.
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destruct b; simpl; rewrite K; rewrite IHw;
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inversion I; inversion J; reflexivity.
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rewrite H4; try rewrite H1; try rewrite H; reflexivity.
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Qed.
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Lemma subsequence_length {X: Type} :
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forall (u v: list X), subsequence u v -> length v <= length u.
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Proof.
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intros u v. generalize u. induction v; intro u0; intro H. apply Nat.le_0_l.
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apply subsequence_eq_def_1 in H. apply subsequence_eq_def_2 in H.
|
|
destruct H. destruct H. destruct H. apply subsequence_eq_def_3 in H0.
|
|
apply IHv in H0. simpl. apply Nat.le_succ_l. rewrite H.
|
|
rewrite app_length. apply Nat.lt_lt_add_l.
|
|
rewrite <- Nat.le_succ_l. simpl. rewrite <- Nat.succ_le_mono.
|
|
assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_eq {X: Type} :
|
|
forall (u v: list X),
|
|
subsequence u v -> subsequence v u -> u = v.
|
|
Proof.
|
|
intro u. induction u; intro v; intros H I;
|
|
apply subsequence_eq_def_1 in H; apply subsequence_eq_def_1 in I.
|
|
|
|
destruct v. reflexivity.
|
|
apply subsequence2_nil_cons_r in H. contradiction H.
|
|
destruct v. apply subsequence2_nil_cons_r in I. contradiction I.
|
|
|
|
destruct H. destruct H. destruct I. destruct H1.
|
|
destruct x0. apply O_S in H. contradiction H.
|
|
destruct x1. apply O_S in H1. contradiction H1.
|
|
destruct b; destruct b0.
|
|
|
|
assert (subsequence2 u v). exists x0.
|
|
split; inversion H; inversion H0; reflexivity.
|
|
assert (subsequence2 v u). exists x1.
|
|
split; inversion H1; inversion H2; reflexivity.
|
|
apply subsequence_eq_def_2 in H3; apply subsequence_eq_def_3 in H3.
|
|
apply subsequence_eq_def_2 in H4; apply subsequence_eq_def_3 in H4.
|
|
apply IHu in H4. rewrite H4. inversion H0. reflexivity. assumption.
|
|
|
|
assert (subsequence2 u v). exists x0.
|
|
split; inversion H; inversion H0; reflexivity.
|
|
assert (subsequence2 v (a::u)). exists x1.
|
|
split; inversion H1; inversion H2; reflexivity.
|
|
assert (subsequence u (a::u)). apply subsequence_trans with (l2 := v);
|
|
apply subsequence_eq_def_3; apply subsequence_eq_def_2; assumption.
|
|
apply subsequence_length in H5. apply Nat.nle_succ_diag_l in H5.
|
|
contradiction H5.
|
|
|
|
assert (subsequence2 u (x::v)). exists x0.
|
|
split; inversion H; inversion H0; reflexivity.
|
|
assert (subsequence2 v u). exists x1.
|
|
split; inversion H1; inversion H2; reflexivity.
|
|
assert (subsequence v (x::v)). apply subsequence_trans with (l2 := u);
|
|
apply subsequence_eq_def_3; apply subsequence_eq_def_2; assumption.
|
|
apply subsequence_length in H5. apply Nat.nle_succ_diag_l in H5.
|
|
contradiction H5.
|
|
|
|
assert (subsequence2 u (x::v)). exists x0.
|
|
split; inversion H; inversion H0; reflexivity.
|
|
assert (subsequence2 v (a::u)). exists x1.
|
|
split; inversion H1; inversion H2; reflexivity.
|
|
apply subsequence2_cons_r in H3. apply subsequence2_cons_r in H4.
|
|
apply subsequence_eq_def_2 in H3. apply subsequence_eq_def_2 in H4.
|
|
apply subsequence_eq_def_3 in H3. apply subsequence_eq_def_3 in H4.
|
|
apply IHu in H4. rewrite H4 in H0. rewrite H4 in H.
|
|
simpl in H0. assert (subsequence2 v (x::v)). exists x0.
|
|
split. inversion H. reflexivity. assumption.
|
|
apply subsequence_eq_def_2 in H5. apply subsequence_eq_def_3 in H5.
|
|
apply subsequence_length in H5. apply Nat.nle_succ_diag_l in H5.
|
|
contradiction H5. assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_length_eq {X: Type} :
|
|
forall (u v: list X),
|
|
subsequence u v -> length u = length v -> u = v.
|
|
Proof.
|
|
intros u v. intros H I. apply subsequence_eq_def_1 in H.
|
|
destruct H. destruct H. rewrite H0 in I.
|
|
rewrite map_length in I.
|
|
replace (length u) with (length (combine x u)) in I.
|
|
symmetry in I. apply filter_length_forallb in I.
|
|
apply forallb_filter_id in I. rewrite I in H0.
|
|
|
|
assert (J: forall (a: list bool) (b: list X),
|
|
length a = length b -> b = map snd (combine a b)).
|
|
intro a. induction a; intro b; intro J.
|
|
symmetry in J. apply length_zero_iff_nil in J. rewrite J. reflexivity.
|
|
destruct b. inversion J. simpl. rewrite <- IHa. reflexivity.
|
|
inversion J. reflexivity. rewrite H0. apply J. assumption.
|
|
|
|
rewrite combine_length. rewrite H. apply PeanoNat.Nat.min_id.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_rev {X: Type} :
|
|
forall (u v: list X), subsequence u v <-> subsequence (rev u) (rev v).
|
|
Proof.
|
|
assert (MAIN: forall (u v: list X),
|
|
subsequence u v -> subsequence (rev u) (rev v)).
|
|
intros u v. intro H.
|
|
apply subsequence_eq_def_3. apply subsequence_eq_def_2.
|
|
apply subsequence_eq_def_1 in H. destruct H. destruct H.
|
|
exists (rev x). split. rewrite rev_length. rewrite rev_length.
|
|
assumption. rewrite H0.
|
|
|
|
assert (LEMMA : forall (l1: list bool) (l2: list X),
|
|
length l1 = length l2
|
|
-> combine (rev l1) (rev l2) = rev (combine l1 l2)).
|
|
intro l1. induction l1; intro l2; intro I. reflexivity.
|
|
destruct l2. inversion I. inversion I. apply IHl1 in H2.
|
|
simpl.
|
|
assert (LEMMA2 : forall (u w : list bool) (v x : list X),
|
|
length u = length v
|
|
-> combine (u ++ w) (v ++ x) = (combine u v) ++ (combine w x)).
|
|
intro u0. induction u0; intros w v0 x1; intro J.
|
|
symmetry in J. apply length_zero_iff_nil in J. rewrite J.
|
|
reflexivity. destruct v0. inversion J. inversion J.
|
|
apply IHu0 with (w := w) (x := x1) in H3. simpl. rewrite H3.
|
|
reflexivity. rewrite LEMMA2. rewrite IHl1. reflexivity.
|
|
inversion I. reflexivity. rewrite rev_length. rewrite rev_length.
|
|
inversion I. reflexivity. rewrite LEMMA. rewrite <- map_rev.
|
|
assert (LEMMA3: forall v (w: list (bool * X)),
|
|
rev (filter v w) = filter v (rev w)).
|
|
intros v0 w. induction w. reflexivity. simpl. rewrite filter_app.
|
|
simpl. destruct (v0 a). simpl. rewrite IHw. reflexivity.
|
|
rewrite IHw. symmetry. apply app_nil_r. rewrite LEMMA3.
|
|
reflexivity. assumption.
|
|
split. apply MAIN. intro H. apply MAIN in H.
|
|
rewrite rev_involutive in H. rewrite rev_involutive in H.
|
|
assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_map {X Y: Type} :
|
|
forall (u v: list X) (f: X -> Y),
|
|
subsequence u v -> subsequence (map f u) (map f v).
|
|
intros u v. generalize u. induction v; intros u0 f.
|
|
intro. apply subsequence_nil_r. intro H.
|
|
apply subsequence_eq_def_3.
|
|
apply subsequence_eq_def_1 in H. apply subsequence_eq_def_2 in H.
|
|
destruct H. destruct H. destruct H.
|
|
exists (map f x). exists (map f x0). split.
|
|
rewrite <- map_cons. rewrite <- map_app. rewrite H. reflexivity.
|
|
apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
apply IHv. apply subsequence_eq_def_3. assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_double_cons {X: Type} :
|
|
forall (u v: list X) a, subsequence (a::u) (a::v) <-> subsequence u v.
|
|
Proof.
|
|
intros u v a. split; intro H. destruct H. destruct H. destruct H.
|
|
destruct x; destruct x0. symmetry in H0. apply nil_cons in H0.
|
|
contradiction. inversion H0.
|
|
exists l. exists x0. split. inversion H. reflexivity. reflexivity.
|
|
apply PeanoNat.Nat.neq_succ_0 in H. contradiction.
|
|
inversion H0. exists (x1++x::l). exists x0. split. inversion H.
|
|
reflexivity. rewrite <- app_assoc. reflexivity.
|
|
apply subsequence_eq_def_3. exists nil. exists u.
|
|
split. reflexivity. apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_filter {X: Type} :
|
|
forall (u v: list X) f, subsequence (filter f u) v -> subsequence u v.
|
|
Proof.
|
|
intro u. induction u; intros v f; intro H. assumption.
|
|
simpl in H. destruct (f a). assert (K := H).
|
|
apply subsequence_eq_def_1 in H. destruct H. destruct H.
|
|
destruct x. apply O_S in H. contradiction. destruct b.
|
|
destruct v. apply subsequence_nil_r. assert (x0 = a). inversion H0.
|
|
reflexivity. rewrite H1.
|
|
apply subsequence_eq_def_3. exists nil. exists u. split. reflexivity.
|
|
apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
apply IHu with (f := f). rewrite H1 in K.
|
|
apply subsequence_double_cons in K. assumption.
|
|
apply subsequence_cons_l. apply IHu with (f := f).
|
|
apply subsequence_eq_def_3. apply subsequence_eq_def_2.
|
|
exists x. split. inversion H. reflexivity. apply H0.
|
|
apply subsequence_cons_l. apply IHu with (f := f). assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_incl {X: Type} :
|
|
forall (u v: list X), subsequence u v -> incl v u.
|
|
Proof.
|
|
intros u v. intro H. intro a. intro I.
|
|
generalize I. generalize H. generalize u.
|
|
induction v; intros u0; intros J K. inversion K.
|
|
destruct K. rewrite H0 in J.
|
|
apply subsequence_eq_def_1 in J.
|
|
apply subsequence_eq_def_2 in J.
|
|
destruct J. destruct H1. destruct H1. rewrite H1.
|
|
|
|
assert (J: forall (u v : list X) w, In w (u++w::v)).
|
|
intro u1. induction u1; intros v0 w. left. reflexivity.
|
|
right. apply IHu1. apply J. apply IHv.
|
|
|
|
apply subsequence_cons_r in H. assumption. assumption.
|
|
apply subsequence_cons_r in J. assumption. assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_split {X: Type} :
|
|
forall (u v w: list X),
|
|
subsequence (u++v) w
|
|
-> (exists a b, w = a++b /\ (subsequence u a) /\ subsequence v b).
|
|
Proof.
|
|
intros u v w. intro H.
|
|
apply subsequence_eq_def_1 in H. destruct H. destruct H.
|
|
|
|
assert (forall (b: list bool) (u v: list X),
|
|
length b = length (u++v)
|
|
-> exists x y, b = x++y /\ length x = length u /\ length y = length v).
|
|
intros b u0 v0. intro I. rewrite app_length in I.
|
|
exists (firstn (length u0) b). exists (skipn (length u0) b).
|
|
split. symmetry. apply firstn_skipn. split.
|
|
rewrite firstn_length_le. reflexivity. rewrite I.
|
|
apply PeanoNat.Nat.le_add_r. rewrite skipn_length.
|
|
rewrite I. rewrite Nat.add_sub_swap. rewrite PeanoNat.Nat.sub_diag.
|
|
reflexivity. apply le_n.
|
|
apply H1 in H. destruct H. destruct H. destruct H. destruct H2.
|
|
|
|
exists (map snd (filter fst (combine x0 u))).
|
|
exists (map snd (filter fst (combine x1 v))).
|
|
rewrite <- map_app. rewrite <- filter_app.
|
|
|
|
assert (L: forall (g i: list bool) (h j: list X), length g = length h
|
|
-> (combine g h) ++ (combine i j) = combine (g++i) (h++j)).
|
|
intro g. induction g; intros i h j; intro I.
|
|
symmetry in I. apply length_zero_iff_nil in I. rewrite I. reflexivity.
|
|
destruct h. apply PeanoNat.Nat.neq_succ_0 in I. contradiction.
|
|
simpl. rewrite IHg. reflexivity. inversion I. reflexivity.
|
|
rewrite L. rewrite <- H. split. assumption.
|
|
split; apply subsequence_eq_def_3; apply subsequence_eq_def_2;
|
|
[ exists x0 | exists x1]; split; try assumption; reflexivity.
|
|
|
|
assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_split_2 {X: Type} :
|
|
forall (u v w: list X),
|
|
subsequence u (v++w)
|
|
-> (exists a b, u = a++b /\ (subsequence a v) /\ subsequence b w).
|
|
Proof.
|
|
intros u v w. intro H. destruct H. destruct H. destruct H.
|
|
exists (x ++
|
|
flat_map (fun e : X * list X => fst e :: snd e) (combine v x0)).
|
|
exists (
|
|
flat_map (fun e : X * list X => fst e :: snd e)
|
|
(combine w (skipn (length v) x0))).
|
|
split. rewrite H0. rewrite <- app_assoc. apply app_inv_head_iff.
|
|
rewrite <- flat_map_app.
|
|
|
|
assert (L: forall (w y: list X) (z : list (list X)),
|
|
length z = length w + length y ->
|
|
combine (w ++ y) z = combine w z ++ combine y (skipn (length w) z)).
|
|
intros w0. induction w0; intros y z; intro I. reflexivity.
|
|
destruct z. simpl. rewrite combine_nil. reflexivity.
|
|
simpl. rewrite IHw0. reflexivity. inversion I. reflexivity.
|
|
rewrite L. reflexivity. rewrite app_length in H. rewrite H.
|
|
reflexivity. split.
|
|
exists x. exists (firstn (length v) x0). split.
|
|
rewrite firstn_length. rewrite <- H. rewrite app_length.
|
|
rewrite min_l. reflexivity. apply PeanoNat.Nat.le_add_r.
|
|
rewrite combine_firstn_l. reflexivity.
|
|
|
|
exists nil. exists (skipn (length v) x0). split.
|
|
rewrite app_length in H. rewrite skipn_length. rewrite <- H.
|
|
rewrite PeanoNat.Nat.add_sub_swap. rewrite PeanoNat.Nat.sub_diag.
|
|
reflexivity. reflexivity. reflexivity.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_single {X: Type} :
|
|
forall (u: list X) a, In a u -> subsequence u [a].
|
|
Proof.
|
|
intro u. induction u; intro x; intro H. apply in_nil in H. contradiction.
|
|
destruct H. rewrite H. exists nil. exists [u]. split. reflexivity.
|
|
simpl. rewrite app_nil_r. reflexivity. apply subsequence_cons_l.
|
|
apply IHu. assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem subsequence_filter_2 {X: Type} :
|
|
forall (u v: list X) f,
|
|
subsequence u v -> subsequence (filter f u) (filter f v).
|
|
Proof.
|
|
intros u v. generalize u. induction v; intros u0 f; intro H.
|
|
apply subsequence_nil_r.
|
|
|
|
assert (f a = true \/ f a = false).
|
|
destruct (f a); [ left | right ]; reflexivity. destruct H0.
|
|
simpl. rewrite H0.
|
|
replace (a::v) with ([a] ++ v) in H. apply subsequence_split_2 in H.
|
|
destruct H. destruct H. destruct H. destruct H1.
|
|
|
|
assert (subsequence ((filter f x) ++ (filter f x0))
|
|
((filter f [a]) ++ (filter f v))).
|
|
apply subsequence_app. simpl. rewrite H0.
|
|
apply subsequence_incl in H1. apply incl_cons_inv in H1.
|
|
destruct H1.
|
|
assert (In a (filter f x)). apply filter_In. split; assumption.
|
|
apply subsequence_single. assumption. apply IHv. assumption.
|
|
rewrite <- filter_app in H3. rewrite <- H in H3. simpl in H3.
|
|
rewrite H0 in H3. assumption. reflexivity.
|
|
simpl. rewrite H0. apply IHv. apply subsequence_cons_r in H.
|
|
assumption.
|
|
Qed.
|
|
|
|
|
|
|
|
|
|
|
|
(** * Tests
|
|
*)
|
|
|
|
Example test1: subsequence [1;2;3;4;5] [1;3;5].
|
|
Proof.
|
|
unfold subsequence.
|
|
exists [].
|
|
exists [[2];[4];[]]. simpl. easy.
|
|
Qed.
|
|
|
|
Example test2: subsequence [1;2;3;4;5] [2;4].
|
|
Proof.
|
|
unfold subsequence.
|
|
exists [1].
|
|
exists [[3];[5]]. simpl. easy.
|
|
Qed.
|
|
|
|
Example test3: subsequence [1;2;3;4;5] [1;3;5].
|
|
Proof.
|
|
apply subsequence_eq_def_3. apply subsequence_eq_def_2.
|
|
exists [true; false; true; false; true].
|
|
split; reflexivity.
|
|
Qed.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Fixpoint smerge {X: Type} (l s1 s2 : list X) : Prop :=
|
|
match l with
|
|
| nil => s1 = nil /\ s2 = nil
|
|
| hd::tl => match s1, s2 with
|
|
| nil, nil => False
|
|
| nil, _ => hd::tl = s2
|
|
| _, nil => hd::tl = s1
|
|
| hd1::tl1, hd2::tl2 =>
|
|
(hd1 = hd2 /\ hd = hd1 /\ smerge tl tl1 tl2)
|
|
\/ (hd1 <> hd2 /\ hd = hd1 /\ smerge tl tl1 s2)
|
|
\/ (hd1 <> hd2 /\ hd = hd2 /\ smerge tl s1 tl2)
|
|
end
|
|
end.
|
|
|
|
|
|
Theorem smerge_exchange {X: Type}:
|
|
forall (l s1 s2: list X), smerge l s1 s2 -> smerge l s2 s1.
|
|
Proof.
|
|
intro l. induction l; intros s1 s2; intro H.
|
|
destruct s1; destruct s2. split; reflexivity.
|
|
destruct H. symmetry in H0. apply nil_cons in H0. contradiction H0.
|
|
destruct H. symmetry in H. apply nil_cons in H. contradiction H.
|
|
destruct H. symmetry in H. apply nil_cons in H. contradiction H.
|
|
destruct s1; destruct s2. assumption.
|
|
rewrite H. reflexivity. rewrite H. reflexivity.
|
|
destruct H. destruct H. destruct H0.
|
|
rewrite H0. rewrite H. apply IHl in H1. simpl. left.
|
|
split. reflexivity. split. reflexivity. assumption.
|
|
destruct H. destruct H. destruct H0. rewrite H0.
|
|
apply IHl in H1. right. right.
|
|
split. symmetry. assumption. split. reflexivity. assumption.
|
|
destruct H. destruct H0. apply IHl in H1. rewrite H0.
|
|
right. left. split. symmetry. assumption.
|
|
split. reflexivity. assumption.
|
|
Qed.
|
|
|
|
|
|
Theorem smerge_subsequence {X: Type}:
|
|
(forall x y : X, {x = y} + {x <> y})
|
|
-> forall (l s1 s2: list X),
|
|
smerge l s1 s2 -> subsequence l s1.
|
|
Proof.
|
|
intro H. intro l. induction l; intros s1 s2; intro I.
|
|
destruct s1. apply subsequence_nil_r.
|
|
destruct I. symmetry in H0. apply nil_cons in H0. contradiction H0.
|
|
|
|
destruct s1; destruct s2.
|
|
apply subsequence_nil_r. apply subsequence_nil_r.
|
|
assert ({a = x} + {a <> x}). apply H. destruct H0. rewrite e in I.
|
|
rewrite e. simpl in I. rewrite I. apply subsequence_id.
|
|
simpl in I. inversion I. apply n in H1. contradiction H1.
|
|
assert ({a = x} + {a <> x}). apply H. destruct H0. rewrite e in I.
|
|
simpl in I. destruct I. destruct H0. destruct H1. apply IHl in H2.
|
|
rewrite e.
|
|
apply subsequence_eq_def_3. simpl. exists nil. exists l.
|
|
split. easy. apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
assumption.
|
|
destruct H0. destruct H0. destruct H1. apply IHl in H2.
|
|
rewrite e.
|
|
apply subsequence_eq_def_3. simpl. exists nil. exists l.
|
|
split. easy. apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
assumption. destruct H0. destruct H1. apply H0 in H1. contradiction H1.
|
|
destruct I. destruct H0. destruct H1. apply IHl in H2.
|
|
rewrite H1.
|
|
apply subsequence_eq_def_3. simpl. exists nil. exists l.
|
|
split. easy. apply subsequence_eq_def_2. apply subsequence_eq_def_1.
|
|
assumption. destruct H0. destruct H0. destruct H1.
|
|
apply n in H1. contradiction H1.
|
|
destruct H0. destruct H1. apply IHl in H2.
|
|
apply subsequence_cons_l. assumption.
|
|
Qed.
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Theorem smerge_subsequence2 {X: Type}:
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(forall x y : X, {x = y} + {x <> y})
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-> forall (l s1 s2: list X), smerge l s1 s2 -> subsequence l s2.
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Proof.
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intros. apply smerge_exchange in H.
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apply smerge_subsequence with (s2 := s1); assumption.
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Qed.
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Example test4: smerge [1; 2; 3; 2; 1] [1;2;1] [3;2].
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Proof.
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simpl. right. left. split. easy.
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split. reflexivity. right. left.
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split. easy. split. reflexivity.
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right. right. split. easy. split. easy.
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right. right. split; easy.
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Qed.
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