0 infinity open set

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

A set is open relative to a set if is open in . Note that can be any topological space, it need n...

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

Being open relative to X means that there is some open set O′ such that O=O′∩X, and equivalently ...

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