This page is a sub-page of our page on Mathematical Concepts.
Related KMR pages:
• Oscar Reutersvärd
• M.C. Escher
• Homology and Cohomology
A structure that implements openness
is called a topology.
An open set has no boundary.
Every one of its member elements
is always “interior” of it,
that is, each point is contained in a neighborhood of points
that also belong to the open set.
The complement of an open set
is called a closed set.
In contrast to an open set
a closed set has a boundary
and if the closed set is also compact
then it behaves much like a closed interval
with respect to convergence of a sequence:
Any sequence of members that tries to converge