Definition Markov_Sat := forall p, decidable p -> (~~ exists t, p t) -> exists t, p t.
Definition Markov_Eva := forall s, closed s -> ~~ eva s -> eva s.

(* Specifications: *)
Lemma Markov_Post_to_Sat : Markov_Post -> Markov_Sat.
Lemma Markov_Sat_to_Eva : Markov_Sat -> Markov_Eva.
Lemma Markov_Eva_to_Post : Markov_Eva -> Markov_Post.