EDB — 0G6

[0G6] A topology \(𝜏⊆{\mathcal P}(X)\) is a family of subsets of \(X\) that are called open sets. This family enjoys three properties: \(∅,X\) are open; the intersection of a finite number of open sets is an open sets; the union of an arbitrary number of open sets is an open set.

A set \(A\) is closed if \(A^ c\) is open.