Calculate: (the square of x-2x + 1-y) divided by (x + Y-1)

Calculate: (the square of x-2x + 1-y) divided by (x + Y-1)

x^-2x+1-y^2=(x-1)^2-y^2=(x-y-1)(x+y-1) (x^-2x+1-y^2)/(x+y-1)=x-y-1