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begin quote ita"
CHAPTER I [:] Notions from Set Theory [...] 1. SETS AND ELEMENTS. SUBSETS. "end quote
These pages assume that the reader has the book and is reading along.    
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Please read these notes from the beginning to here, and then paragraph 4 of 1.

ELEMENTS OF SETS

I think 'being in a set' - indicated by the symbol - is another concept that is somewhat more subtle that it appears. Because ...

begin quote ita-1-1-4-pg2 "
The symbol must also have other properties (which we don't specify here) that enable us, given certain sets, to construct others.
"end quote

This is also something I missed on my first reading, although I recall various constructions, and I am looking forward very much to looking at those constructions again - keeping in mind the just quoted connection to the symbol .

on to reading 3