krugly1981 (x^2y^3 - y^3) - xy + y = y^3( x^2 - 1) - y( x - 1) = y^3(x - 1)(x + 1) - y(x - 1) =
= ( x - 1)(xy^3 + y^3 - y) = y( x - 1)(xy^2 + y^2 - 1)