(*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 eq_eq_Mmap2_eq {A B C:Type} (f:A→B→C) (ma:monad A) (mb:monad B):
Meq ma → Meq mb → Meq (Mmap2 f ma mb).