fact: Definition CountableT (X : Type) : Prop := exists f : X -> nat, injective f.
imports: Coq(Arith ArithRing ClassicalChoice Description FunctionalExtensionality Lia Relation_Definitions Program.Subset QArith ZArith) ZornsLemma(CSB DecidableDec DependentTypeChoice Finite_sets FiniteTypes FunctionPropertiesEns IndexedFamilies InfiniteTypes)