если x^3+y^3-xy^2-x^2y, то
x^2(x-y)-y^2(x-y)=(x^2-y^2)(x-y)=(x+y)(x-y)(x-y)=(x+y)(x-y)^2
x^3(y-1) - x(y-1)(y-1)(x^3-x) x(y-1)(x^2-1)x(y-1)(x-1)(x+1)
