Standard Library | The Coq Proof Assistant

The Coq Proof Assistant

# 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)).