(-8-b)+(a+23)=-8-b+a+23=a-b+15
(-8-b)-(a+23)=-8-b-a-23=-a-b-31
(x+8)+(y-9)=x+8+y-9=x+y-1
(x+8)-(y-9)=x+8-y+9=x-y+17
(-8-b)+(a+23)=-8-b+a+23=a-b+15
(-8-b)-(a+23)=-8-b-a-23=-a-b-31
(x+8)+(y-9)=x+8+y-9=x+y-1
(x+8)-(y-9)=x+8-y+9=x-y+17