∀ {F : PFunctor.{u_1, u_2}} (motive : PFunctor.Approx.Path F → F.M → Sort u_3) (a : F.A) (i : F.B a) (ps : List F.Idx)
  (x : F.M) (h_1 : (x : F.M) → motive [] x)
  (h_2 : (a : F.A) → (i : F.B a) → (ps : List F.Idx) → (x : F.M) → motive (⟨a, i⟩ :: ps) x),
  (match ⟨a, i⟩ :: ps, x with
    | [], x => h_1 x
    | ⟨a, i⟩ :: ps, x => h_2 a i ps x) =
    h_2 a i ps x