Let T be a non empty topological structure.
T is a homeomorphism.
Let T be a non empty topological space and let p be a point of T . Note that every neighbourhood of p is non empty. The following proposition is true For every non empty topological space T and for every point p of T holds T is a neighbourhood of p . Let T be a non empty topological space and let p be a point of T . Note that there exists a neighbourhood of p which is non empty and open.