A point x is called an accumulation point of a set E provided it is a point of closure E-{x}
1) Show that the set E' of accumulation points of E is a closed set.
2) Show that E'' = E U E'
First of all is E-{x} = E\{x}? Second of all can you show us an attempt (I should not have answered your in other question in so much detail so I apologize the the OPs)?