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_weaken {S} {M} `{PredLift M} {X} {Pre : S -> Prop} (Post : S -> Prop) {Post' : S -> Prop} (P : X -> Prop) : forall m, (forall s, Post s -> Post' s) -> state_plift Pre Post P m -> state_plift Pre Post' P m.