Library Coq.Logic.ClassicalChoice
This file provides classical logic and functional choice; this
    especially provides both indefinite descriptions and choice functions
    but this is weaker than providing epsilon operator and classical logic
    as the indefinite descriptions provided by the axiom of choice can
    be used only in a propositional context (especially, they cannot
    be used to build choice functions outside the scope of a theorem
    proof) 
 
 This file extends ClassicalUniqueChoice.v with full choice.
    As ClassicalUniqueChoice.v, it implies the double-negation of
    excluded-middle in Set and leads to a classical world populated
    with non computable functions. Especially it conflicts with the
    impredicativity of Set, knowing that true<>false in Set.  
Require Export ClassicalUniqueChoice.
Require Export RelationalChoice.
Require Import ChoiceFacts.
Set Implicit Arguments.
Definition subset (U:Type) (P Q:U->Prop) : Prop := forall x, P x -> Q x.
Theorem singleton_choice :
forall (A : Type) (P : A->Prop),
(exists x : A, P x) -> exists P' : A->Prop, subset P' P /\ exists! x, P' x.
Theorem choice :
forall (A B : Type) (R : A->B->Prop),
(forall x : A, exists y : B, R x y) ->
exists f : A->B, (forall x : A, R x (f x)).
