Open Set

• is a generalization of an open interval in the real line
• an open set is identical to its interior

Closed Set

• is a generalization of a closed interval in the real line
• a closed set contains all its limit points

Clopen Set

• a clopen set is both open and closed

Definitions

• Topological Spaces (Open Sets - Closed Sets - Clopen Sets - Closures)
• Totally Boundedness)