Can you help me to solve this exercise ?

If a is any subset of R^p, then there exists a countable subset C of A such that if x in A

and epsilon > 0 , then there is an element z in C such that ||x-z|| < epsilon . Hence every elements of A is either in C or is a cluster point of C

This exercise from the elements of real analysis for Robert G.Bartle

I need your help as soon as you can

Miss_Lolitta