nLab annulus



topology (point-set topology, point-free topology)

see also differential topology, algebraic topology, functional analysis and topological homotopy theory


Basic concepts

Universal constructions

Extra stuff, structure, properties


Basic statements


Analysis Theorems

topological homotopy theory


An (open) annulus is a topological space that is homeomorphic to the disk with an interior point removed: D 2{0}D^2 \setminus \{0\}.

An often used model for the corresponding closed annulus is the subspace {(x,y)1x 2+y 24} 2\{(x,y)\mid 1\leq x^2 + y^2 \leq 4\} \subset \mathbb{R}^2, of the plane consisting of the point lying between a unit circle and a circle of radius 2, both centred on the origin.

Last revised on November 18, 2014 at 22:34:09. See the history of this page for a list of all contributions to it.