Definition bijection {X Y} (f : X -> Y) : Prop :=
exists g : Y -> X,
(forall x, g (f x) = x) /\
(forall y, f (g y) = y).

Lemma uniform_bind_bijection {X Y} `{EqDec X, EqDec Y} (f : X -> Y) (d : dist X) :
uniform d -> bijection f ->
uniform (mbind d (fun x => mreturn (f x))).