constructor
case h
x : ℝ
⊢ (∃ x_1, (3 ≤ x_1 ∧ x_1 ≤ 5) ∧ x_1 ^ 2 + 3 = x) ↔ 12 ≤ x ∧ x ≤ 28
case h.mp
x : ℝ
⊢ (∃ x_1, (3 ≤ x_1 ∧ x_1 ≤ 5) ∧ x_1 ^ 2 + 3 = x) → 12 ≤ x ∧ x ≤ 28

case h.mpr
x : ℝ
⊢ 12 ≤ x ∧ x ≤ 28 → ∃ x_1, (3 ≤ x_1 ∧ x_1 ≤ 5) ∧ x_1 ^ 2 + 3 = x