Let X be a set. A topology on X is acollection \(\tau \)of subsets of X, for which one of these does not hold:
The set X itself and the empty set \(\phi\) are in \(\tau\)
Arbitrary unions\( \bigcup_{}^{}\cup\) of elememnts of \(\tau\) are in \(\tau\)
Finite intersection \(\bigcap\cup_k\) of elements of \(\tau\) are in \(\tau\)
—>> The set X x X is also a member of \(\chi\)
