I know this work is correct but I have one question circled in black marker could someone please answer it for me

Please state all definitions and theorems that you will need: Definition 5.4.1 Let f: D -> R . We say that f is uniformly continuous on D if for every & > 0 there exists a 6 > 0 such that If() - f(y)) 0 and choose 61 > 0 . Then, if x, y E D and (x - y) 0 . Then, if x, y E D and |x - y|