Puncture (topology)

{{Short description|Removal of points from a manifold}}

{{distinguish|Puncturing (coding theory)}}

In topology, puncturing a manifold is removing a finite set of points from that manifold.{{sfn|Seifert|Threlfall|1980|p=29}} The set of points can be small as a single point. In this case, the manifold is known as once-punctured. With the removal of a second point, it becomes twice-punctured, and so on.

Examples of punctured manifolds include the open disk (which is a sphere with a single puncture), the cylinder (which is a sphere with two punctures),{{sfn|Seifert|Threlfall|1980|p=29}} and the Möbius strip (which is a projective plane with a single puncture).{{sfn|Seifert|Threlfall|1980|p=12}}