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Some examples related to colorings

Michael van Hartskamp, Jan van Mill (2000)

Commentationes Mathematicae Universitatis Carolinae

We complement the literature by proving that for a fixed-point free map f : X X the statements (1) f admits a finite functionally closed cover 𝒜 with f [ A ] A = for all A 𝒜 (i.e., a coloring) and (2) β f is fixed-point free are equivalent. When functionally closed is weakened to closed, we show that normality is sufficient to prove equivalence, and give an example to show it cannot be omitted. We also show that a theorem due to van Mill is sharp: for every n 2 we construct a strongly zero-dimensional Tychonov space...

Some Properties of the Sorgenfrey Line and the Sorgenfrey Plane

Adam St. Arnaud, Piotr Rudnicki (2013)

Formalized Mathematics

We first provide a modified version of the proof in [3] that the Sorgenfrey line is T1. Here, we prove that it is in fact T2, a stronger result. Next, we prove that all subspaces of ℝ1 (that is the real line with the usual topology) are Lindel¨of. We utilize this result in the proof that the Sorgenfrey line is Lindel¨of, which is based on the proof found in [8]. Next, we construct the Sorgenfrey plane, as the product topology of the Sorgenfrey line and itself. We prove that the Sorgenfrey plane...

Spaces of continuous functions, Σ -products and Box Topology

J. Angoa, Angel Tamariz-Mascarúa (2006)

Commentationes Mathematicae Universitatis Carolinae

For a Tychonoff space X , we will denote by X 0 the set of its isolated points and X 1 will be equal to X X 0 . The symbol C ( X ) denotes the space of real-valued continuous functions defined on X . κ is the Cartesian product κ with its box topology, and C ( X ) is C ( X ) with the topology inherited from X . By C ^ ( X 1 ) we denote the set { f C ( X 1 ) : f can be continuously extended to all of X } . A space X is almost- ω -resolvable if it can be partitioned by a countable family of subsets in such a way that every non-empty open subset of X has a non-empty...

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