c-(a-b)= c-a+b
c+(a+b)= c+a+b
c-(a+b)= c-a-b
-c-(-a-b)= -c+a+b
(a-b)+(c-d)= a-b+c-d
(-a-b)-(c-d)= -a-b-c+d
x+(a-b)-(c-d)= x+a-b-c+d
d-(a+b)-(c-d)= d-a-b-c+d
c-(a-b)= c-a+b
c+(a+b)= c+a+b
c-(a+b)= c-a-b
-c-(-a-b)= -c+a+b
(a-b)+(c-d)= a-b+c-d
(-a-b)-(c-d)= -a-b-c+d
x+(a-b)-(c-d)= x+a-b-c+d
d-(a+b)-(c-d)= d-a-b-c+d