(x - y)*(x + y) + x - y
1*(x - y)*(x + 1 + y)
(1*(x - y))*(x + (1 + y))
2 2 x + x - y - y
x + x^2 - y - y^2
(x - y)*(1 + x + y)
x - y + (x + y)*(x - y)