(2x-y+1)(2x+y-1)=[2x-(y-1)][2x+(y-1)]=(2x)^2-(y-1)^2=4x^2-y^2+2y-1
(2x-y+1)(2x+y-1)=[2x-(y-1)][2x+(y-1)]=(2x)^2-(y-1)^2=4x^2-y^2+4y-1
(2x-y+1)(2x+y-1)=[2x-(y-1)][(2x+(y-1)]=4x^2-(y-1)^2=4x^2-y^2+2y-1
