[(x + 1) − y]^2

[(x + 1) − y]^2

This is just a perfect square.

$[(x + 1) − y]^2\\ = (x+1)^2\;\;-\;\;2*(x+1)*y\;\;+\;\;y^2\\ = (x^2+2x+1)\;\;-\;\;2y(x+1)\;\;+\;\;y^2\\ = x^2+2x+1\;\;-\;\;2xy-2y\;\;+\;\;y^2\\$