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(*                 The Calculus of Inductive Constructions                  *)
(*                                                                          *)
(*                                Projet Coq                                *)
(*                                                                          *)
(*                     INRIA        LRI-CNRS        ENS-CNRS                *)
(*              Rocquencourt         Orsay          Lyon                    *)
(*                                                                          *)
(*                                 Coq V6.3                                 *)
(*                               July 1st 1999                              *)
(*                                                                          *)
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(*                                ListSet.v                                 *)
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(* A Library for finite sets, implemented as lists *)
(* A Library with similar interface will soon be available under the name TreeSet in the theories/TREES directory *)
(* PolyList is loaded, but not exported *)
(* This allow to "hide" the definitions, functions and theorems of PolyList and to see only the ones of ListSet *)
Set Implicit Arguments.
Unset Strict Implicit.
Section first_definitions.
Variable A : Set.
Hypothesis Aeq_dec : forall x y : A, {x = y} + {x <> y}.
Definition set := list A.
Definition empty_set := nil (A:=A).
Fixpoint set_add (a : A) (x : set) {struct x} : set :=
match x with
| nil => a :: nil
| a1 :: x1 =>
match Aeq_dec a a1 with
| left _ => a1 :: x1
| right _ => a1 :: set_add a x1
end
end.
Fixpoint set_mem (a : A) (x : set) {struct x} : bool :=
match x with
| nil => false
| a1 :: x1 =>
match Aeq_dec a a1 with
| left _ => true
| right _ => set_mem a x1
end
end.
(* If a belongs to x, removes a from x. If not, does nothing *)
Fixpoint set_remove (a : A) (x : set) {struct x} : set :=
match x with
| nil => empty_set
| a1 :: x1 =>
match Aeq_dec a a1 with
| left _ => set_remove a x1
| right _ => a1 :: set_remove a x1
end
end.
Fixpoint set_inter (x : set) : set -> set :=
match x with
| nil => fun y => nil (A:=A)
| a1 :: x1 =>
fun y =>
if set_mem a1 y then a1 :: set_inter x1 y else set_inter x1 y
end.
Fixpoint set_union (x y : set) {struct y} : set :=
match y with
| nil => x
| a1 :: y1 => set_add a1 (set_union x y1)
end.
(* returns the set of all els of x that does not belong to y *)
Fixpoint set_diff (x : set) : set -> set :=
fun y =>
match x with
| nil => nil (A:=A)
| a1 :: x1 =>
if set_mem a1 y then set_diff x1 y else set_add a1 (set_diff x1 y)
end.
(** Inductive set_In : A -> set -> Prop := set_In_singl : (a:A)(x:set)(set_In a (cons a (nil A))) | set_In_add : (a,b:A)(x:set)(set_In a x)->(set_In a (set_add b x)) . **)
Definition set_In : A -> set -> Prop := In (A:=A).

Lemma Set_remove1 : forall (B : set) (x : A), ~ set_In x (set_remove x B).
intro; intro.