EDB — 0J3

[0J3] A subset \(K⊆ X\) is compact ¹ if, from every family of open sets \((A_ i)_{i∈ I}\) whose union \(⋃_{i∈ I}A_ i\) covers \(K\), we can choose a finite number \(J⊂ I\) of open set whose union \(⋃_{i∈ J}A_ i\) covers \(K\).