3 Are there constant functions x3(x1, x2) and x4(x1, x2) which are defined by f(x) = 0?

Let be given f(x1, x2, x3x4) = x1x2x3x4 ∨ x1x2x3 ∨ x1x2x3x4 ∨ x1x2x3x4.