Definition Mbind {A B:Type} (m:monad A) f :=
  (λ st, let (st',x) := Meval m st in
         let m' := f x in Meval m' st'):monad B.Infix ">>=" := Mbind (at level 15, left associativity) : monad_scope.

Lemma Mbind_ind {A:Type} (ma:monad A) (f:A→monad A) (P:A → Prop): (∀ st, P (snd (ma st))) → (∀ (a:A), P a → ∀ st, P (snd ((f a) st))) → ∀ st, P (snd ((ma>>=f) st)).