∀ {β : Type u_1} (motive : ForInStep β → Sort u_2) (b : β) (h_1 : (b : β) → motive (ForInStep.done b))
  (h_2 : (b : β) → motive (ForInStep.yield b)),
  (match ForInStep.yield b with
    | ForInStep.done b => h_1 b
    | ForInStep.yield b => h_2 b) =
    h_2 b