simp only [Set.mem_setOf_eq]
case h.mpr
x : ℤ
hor :
  x = -7 ∨
    x = -6 ∨ x = -5 ∨ x = -4 ∨ x = -3 ∨ x = -2 ∨ x = -1 ∨ x = 0 ∨ x = 1 ∨ x = 2 ∨ x = 3 ∨ x = 4 ∨ x = 5 ∨ x = 6 ∨ x = 7
⊢ x ∈ {x | |3 * x| < 24}
case h.mpr
x : ℤ
hor :
  x = -7 ∨
    x = -6 ∨ x = -5 ∨ x = -4 ∨ x = -3 ∨ x = -2 ∨ x = -1 ∨ x = 0 ∨ x = 1 ∨ x = 2 ∨ x = 3 ∨ x = 4 ∨ x = 5 ∨ x = 6 ∨ x = 7
⊢ |3 * x| < 24