0 infinity open set

If Y is closed relative to X and p is a border point relative to X, then p has a neighborhood ent...

A set M in a topological space is relatively open (relatively closed) with respect to E if and on...

In a metric space—that is, when a distance function is defined—open sets are the sets that, with ...

A subset of a topological space is relatively open if it is an open set in some relative topology...

The neighborhood definition of open sets generalizes to relatively open sets. First, we define re...