(* 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_plus (T: Set) (f g: T -> nat) (t: ne_tree.T T):
expec (fun x => plus (f x) (g x)) t = expec f t + expec g t.