∀ (x : SetTheory.PGame) (α β : Type u_1) (a : α → SetTheory.PGame) (a_1 : β → SetTheory.PGame)
  (motive : x.memᵣ (SetTheory.PGame.mk α β a a_1) → Prop) (x_1 : x.memᵣ (SetTheory.PGame.mk α β a a_1)),
  (∀ (i : (SetTheory.PGame.mk α β a a_1).RightMoves) (hi : x.Identical ((SetTheory.PGame.mk α β a a_1).moveRight i)),
      motive ⋯) →
    motive x_1