4 4 x - y
x^4 - y^4
1*(x + y)*(x - y)*(x + I*y)*(x - I*y)
(((1*(x + y))*(x - y))*(x + i*y))*(x - i*y)
/ 2 2\ (x + y)*(x - y)*\x + y /
(x + y)*(x - y)*(x^2 + y^2)