∀ {R : Type u_1} [inst : Add R] [inst_1 : Neg R] [inst_2 : Zero R] [inst_3 : One R]
  (add_assoc : ∀ (a b c : R), a + b + c = a + (b + c)) (zero_add : ∀ (a : R), 0 + a = a)
  (neg_add_cancel : ∀ (a : R), -a + a = 0) (n : ℕ), (Int.negSucc n).castDef = -↑(n + 1)