Definition StateT (S : Type) (M : Type -> Type) (X : Type) : Type :=
  S -> M (X * S)%type.Definition StateT_ret {S} {M} `{Monad M} {X} :
  X -> StateT S M X :=
  fun x s => mreturn (x, s).Definition StateT_bind {S} {M} `{Monad M} {X Y} :
  StateT S M X ->
  (X -> StateT S M Y) ->
  StateT S M Y :=
  fun mx f s =>
    mbind (mx s) (fun '(x, s') => f x s').Global Instance StateT_Monad {M} {S} `{Monad M} : Monad (StateT S M) := {|
  mreturn A := StateT_ret;
  mbind X Y := StateT_bind
  |}.Definition get {S M} `{Monad M}: StateT S M S :=
  fun s => mreturn(s,s).Definition put {S M} `{Monad M} (st : S) :
  StateT S M unit := fun s => mreturn(tt, st).Definition state_plift {S} {M} `{Monad M} `{PredLift M} {X} (Pre Post : S -> Prop) (P : X -> Prop) :
  StateT S M X -> Prop :=
  fun mx =>
    forall s, Pre s -> plift (fun '(x, s') => P x /\ Post s') (mx s).

Lemma state_plift_bind {S X Y} {M} `{Monad M} `{PredLift M} {Pre : S -> Prop} (Mid : S -> Prop) {Post : S -> Prop} (P: X -> Prop) {Q: Y -> Prop} {mx : StateT S M X} {f : X -> StateT S M Y} : state_plift Pre Mid P mx -> (forall x, P x -> state_plift Mid Post Q (f x)) -> state_plift Pre Post Q (mbind mx f).