topology (point-set topology, point-free topology)
see also differential topology, algebraic topology, functional analysis and topological homotopy theory
Basic concepts
fiber space, space attachment
Extra stuff, structure, properties
Kolmogorov space, Hausdorff space, regular space, normal space
sequentially compact, countably compact, locally compact, sigma-compact, paracompact, countably paracompact, strongly compact
Examples
Basic statements
closed subspaces of compact Hausdorff spaces are equivalently compact subspaces
open subspaces of compact Hausdorff spaces are locally compact
compact spaces equivalently have converging subnet of every net
continuous metric space valued function on compact metric space is uniformly continuous
paracompact Hausdorff spaces equivalently admit subordinate partitions of unity
injective proper maps to locally compact spaces are equivalently the closed embeddings
locally compact and second-countable spaces are sigma-compact
Theorems
Analysis Theorems
An (open) annulus is a topological space that is homeomorphic to the disk with an interior point removed: $D^2 \setminus \{0\}$.
An often used model for the corresponding closed annulus is the subspace $\{(x,y)\mid 1\leq x^2 + y^2 \leq 4\} \subset \mathbb{R}^2$, 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.