rfl
case Ret
E F : Type → Type
T R : Type
h : E ~> OptionT (Fitree F)
k : T → Fitree E R
r✝ : T
⊢ interpOption h (bind (Ret r✝) k) =
    bind (interpOption h (Ret r✝)) fun x? =>
      match x? with
      | some x => interpOption h (k x)
      | none => ret none
no goals