{G : Type u_9} →
  {P : Type u_10} →
    [inst : VAdd G P] →
      {motive : IsLeftCancelVAdd G P → Sort u} →
        (t : IsLeftCancelVAdd G P) →
          ((left_cancel' : ∀ (a : G) (b c : P), a +ᵥ b = a +ᵥ c → b = c) → motive ⋯) → motive t