\(\underline{Def:}\)A topology space
\(X=(\underline{X},\eth_{x})\)consists of a set \(\underline{X}\),called the underlying space of \(X\) ,and a family \(\eth_{x}\)of subsets of \(X\)(ie.\(\eth_{x}\subset P(\underline{X})\))
原文：https://www.cnblogs.com/zonghanli/p/12232602.html