Challenge problem:

Let f be a function :http://www.mathhelpforum.com/math-he...a5938e6ffd.png

Prove that:

If, a, is not an accumulation point of A,then there exists an mεR,such that for all ε>0 there exists a δ>0 such that :

for all ,x: http://www.mathhelpforum.com/math-he...2953ecd1dc.png and

Moderator edit:Approved Challenge question.