rintro (h1 | h2)
case mp
x : ℝ
⊢ x.cos = 0 ∨ x.cos ^ 2 = 1 / 2 ∨ (3 * x).cos = 0 → x.cos ^ 2 = 1 / 2 ∨ (3 * x).cos = 0
case mp.inl
x : ℝ
h1 : x.cos = 0
⊢ x.cos ^ 2 = 1 / 2 ∨ (3 * x).cos = 0

case mp.inr
x : ℝ
h2 : x.cos ^ 2 = 1 / 2 ∨ (3 * x).cos = 0
⊢ x.cos ^ 2 = 1 / 2 ∨ (3 * x).cos = 0