From Undecidability.Synthetic Require Import DecidabilityFacts SemiDecidabilityFacts.
From Undecidability.Shared Require Import embed_nat.
Local Notation "'if!' x 'is' p 'then' a 'else' b" := (match x with p => a | _ => b end) (at level 0, p pattern).
Definition enumerator__T' X f := forall x : X, exists n : nat, f n = Some x.
Notation enumerator__T f X := (enumerator__T' X f).
Definition enumerable__T X := exists f : nat -> option X, enumerator__T f X.

Theorem dec_count_enum' X (p : X -> Prop) :
decidable p -> enumerable__T X -> enumerable (fun x => ~ p x).