(* misc expec *)

Add Parametric Morphism (A: Set): (@expec A)
  with signature (@ext_eq A nat) ==> (@ext_eq (ne_tree.T A) R)
  as expec_ext_morph.

Lemma expec_0_inv (T: Set) (f: T -> nat) (t: ne_tree.T T): expec f t = 0 -> forall x, ne_tree.In x t -> f x = 0%nat.