A-(b+c) ,(a+b)-c ,a-(b-c)-d
A+(b-c+d)=a+b-c+d 2)a -(b-c+d)=a-b+c-d 3)a-(b-c-d)=a-b+c+d 4)a-(b+(c-d+k ))=a-(b+c-d+k)=a-b-c+d
A-b-c .a+b-c .a-b+c-d