(*Definition Mmake {A B:Type} (f:A→B) x:= Mreturn (f x).*)
Definition Mupdate (f:nat→nat) := (λ st, ((f st),tt)):monad unit.

Lemma mono_mono_Mmap2_mono {A B C:Type} (f: A → B → C) ma mb:
Mmono ma → Mmono mb → Mmono (Mmap2 f ma mb).