spiderg Ax+ay-x^2-2xy-y^2=a(x+y)-(x+y)^2=(x+y)(a-x-y)
a^2-2ab+b^2-a+b=(b-a)^2+(b-a)=(b-a)(b-a+1)
a^2-b^2-c^2+2bc=a^2-(b-c)^2=(a-b+c)(a+b-c)