Require Export Undecidability.Synthetic.Definitions Undecidability.Synthetic.ReducibilityFacts.
Definition undecidable {X} (p : X -> Prop) :=
decidable p -> decidable (HaltTM 1).

Lemma undecidability_from_reducibility {X} {p : X -> Prop} {Y} {q : Y -> Prop} :
undecidable p -> p ⪯ q -> undecidable q.