Let f

-->R and xo is a cluster point of D. Prove that f has a limit at xo if for each epsilon>0 there is a neighborhood Q of xo such that for all x,y belonging to QintersectD x=/=xo, y=/=xo, we have |f(x)-f(y)|<epsilon.

I have an exam coming up in a week and I don't even know where to start with such weird problems.

I found a proof of this statement on the web (Since we don't have a solution manual), but it is very long and complicated..using many things that we have not used in this course. I was hoping someone could help me get an easier proof so that if such a problem appeared on my exam, I might actually have a chance because there is no way I could come up with the proof I found. Thanks