Find the minimum sum-of-products expressions for each of these functions.
(a) f1(A, B, C) = m1 + m2 + m5 + m7
(b) f2(d, e, f ) = Σ m(1, 5, 6, 7)
(c) f4(a, b, c) = m0 + m2 + m3 + m7