Definition π (u : term) s := eva (u (tenc s)).Definition rel_eq P Q := forall x, P x <-> Q x.Definition rel_incl P Q := forall x, P x -> Q x.Notation "a <𝐦 b" := (lt_mdegree a b) (at level 40).Instance rel_eq_equiv : Equivalence rel_eq.Definition creative P := recognisable P /\ productive (complement P).

Lemma productive_K : productive (fun s : term => ~ eva (s (tenc s))).