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
The Scott topology on a preordered set is the topology in which the open subsets (called Scott-open) are precisely those whose characteristic functions (from the given preorder into the preorder of truth values) preserve directed joins (and this makes them necessarily monotonic).
This in fact ensures that, in general, the continuous functions between preorders with Scott topologies are precisely those (necessarily monotonic) functions between them which preserve directed joins (called Scott-continuous). The poset of truth values itself, therefore, when equipped with the Scott topology, becomes the open-set classifier, Sierpinski space.
In the category of topological spaces (see at separation axiom), the injective objects are precisely those given by Scott topologies on continuous lattices; as locales these are locally compact and spatial.
Last revised on October 11, 2019 at 12:54:39. See the history of this page for a list of all contributions to it.