simp [ExceptT.bind, ExceptT.mk, ExceptT.bindCont]
case Vis
T R : Type
k : T → Fitree UBE R
T✝ : Type
e✝ : UBE T✝
k✝ : T✝ → Fitree UBE T
ih :
  ∀ (a : T✝),
    Fitree.interp UBE.handle (Fitree.bind (k✝ a) k) =
      Fitree.bind (Fitree.interp UBE.handle (k✝ a)) fun x =>
        match x with
        | Except.error ε => Fitree.ret (Except.error ε)
        | Except.ok x => Fitree.interp UBE.handle (k x)
⊢ Fitree.bind (UBE.handle T✝ e✝) (ExceptT.bindCont fun t => Fitree.interp UBE.handle (Fitree.bind (k✝ t) k)) =
    Fitree.bind (UBE.handle T✝ e✝) fun x =>
      Fitree.bind (ExceptT.bindCont (fun t => Fitree.interp UBE.handle (k✝ t)) x) fun x =>
        match x with
        | Except.error ε => Fitree.ret (Except.error ε)
        | Except.ok x => Fitree.interp UBE.handle (k x)
case Vis
T R : Type
k : T → Fitree UBE R
T✝ : Type
e✝ : UBE T✝
k✝ : T✝ → Fitree UBE T
ih :
  ∀ (a : T✝),
    Fitree.interp UBE.handle (Fitree.bind (k✝ a) k) =
      Fitree.bind (Fitree.interp UBE.handle (k✝ a)) fun x =>
        match x with
        | Except.error ε => Fitree.ret (Except.error ε)
        | Except.ok x => Fitree.interp UBE.handle (k x)
⊢ (Fitree.bind (UBE.handle T✝ e✝) fun x =>
      match x with
      | Except.ok a => Fitree.interp UBE.handle (Fitree.bind (k✝ a) k)
      | Except.error e => Fitree.ret (Except.error e)) =
    Fitree.bind (UBE.handle T✝ e✝) fun x =>
      Fitree.bind
        (match x with
        | Except.ok a => Fitree.interp UBE.handle (k✝ a)
        | Except.error e => Fitree.ret (Except.error e))
        fun x =>
        match x with
        | Except.error e => Fitree.ret (Except.error e)
        | Except.ok x => Fitree.interp UBE.handle (k x)