summaryrefslogtreecommitdiff
path: root/theories/Sets/Permut.v
blob: 4380f10c9a3aedb933f1aacedb923a5b7d6d628a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(*i $Id: Permut.v 10616 2008-03-04 17:33:35Z letouzey $ i*)

(* G. Huet 1-9-95 *)

(** We consider a Set [U], given with a commutative-associative operator [op],
    and a congruence [cong]; we show permutation lemmas *)

Section Axiomatisation.

  Variable U : Type.
  Variable op : U -> U -> U.
  Variable cong : U -> U -> Prop.

  Hypothesis op_comm : forall x y:U, cong (op x y) (op y x).
  Hypothesis op_ass : forall x y z:U, cong (op (op x y) z) (op x (op y z)).

  Hypothesis cong_left : forall x y z:U, cong x y -> cong (op x z) (op y z).
  Hypothesis cong_right : forall x y z:U, cong x y -> cong (op z x) (op z y).
  Hypothesis cong_trans : forall x y z:U, cong x y -> cong y z -> cong x z.
  Hypothesis cong_sym : forall x y:U, cong x y -> cong y x.

  (** Remark. we do not need: [Hypothesis cong_refl : (x:U)(cong x x)]. *)

  Lemma cong_congr :
    forall x y z t:U, cong x y -> cong z t -> cong (op x z) (op y t).
  Proof.
    intros; apply cong_trans with (op y z).
    apply cong_left; trivial.
    apply cong_right; trivial.
  Qed.
  
  Lemma comm_right : forall x y z:U, cong (op x (op y z)) (op x (op z y)).
  Proof.
    intros; apply cong_right; apply op_comm.
  Qed.
  
  Lemma comm_left : forall x y z:U, cong (op (op x y) z) (op (op y x) z).
  Proof.
    intros; apply cong_left; apply op_comm.
  Qed.
  
  Lemma perm_right : forall x y z:U, cong (op (op x y) z) (op (op x z) y).
  Proof.
    intros.
    apply cong_trans with (op x (op y z)).
    apply op_ass.
    apply cong_trans with (op x (op z y)). 
    apply cong_right; apply op_comm.
    apply cong_sym; apply op_ass.
  Qed.

  Lemma perm_left : forall x y z:U, cong (op x (op y z)) (op y (op x z)).
  Proof.
    intros.
    apply cong_trans with (op (op x y) z).
    apply cong_sym; apply op_ass.
    apply cong_trans with (op (op y x) z).
    apply cong_left; apply op_comm.
    apply op_ass.
  Qed.
  
  Lemma op_rotate : forall x y z t:U, cong (op x (op y z)) (op z (op x y)).
  Proof.
    intros; apply cong_trans with (op (op x y) z).
    apply cong_sym; apply op_ass.
    apply op_comm.
  Qed.

  (** Needed for treesort ... *)
  Lemma twist :
    forall x y z t:U, cong (op x (op (op y z) t)) (op (op y (op x t)) z).
  Proof.
    intros.
    apply cong_trans with (op x (op (op y t) z)).
    apply cong_right; apply perm_right.
    apply cong_trans with (op (op x (op y t)) z).
    apply cong_sym; apply op_ass.
    apply cong_left; apply perm_left.
  Qed.

End Axiomatisation.