n : ℕ
⊢ n % 2 + 2 * div2 n = n
n : ℕ
⊢ div2 n = n / 2
refine'
  Nat.eq_of_mul_eq_mul_left (by decide)
    (Nat.add_left_cancel (Eq.trans _ (Nat.mod_add_div n 2).symm))
no goals
n : ℕ
⊢ n % 2 + 2 * div2 n = n
rw [mod_two_of_bodd, bodd_add_div2]
no goals
n : ℕ
⊢ 0 < 2
decide