x(1−x2)(1+y2)2+y(1−y2)(1+x2)2−4xy(1+y2)(1+x2)x(1-x^2)(1+y^2)^2+y(1-y^2)(1+x^2)^2-4xy(1+y^2)(1+x^2)x(1−x2)(1+y2)2+y(1−y2)(1+x2)2−4xy(1+y2)(1+x2)
