例 & & F=POR=ABC·.ABC+ABC·ABC A BC+ABC+ABC+ ABc =ml+m2+m4+m7=∑m(12,4,7)例： M C N PQR F = PQR = A B C A BC + ABC  AB C = m 1 + m 2 + m 4 + m 7 =  m ( 1 , 2 , 4 , 7 ) = A B C + AB C + A B C + ABC