English

Selectors of discrete coarse spaces

General Topology 2021-03-19 v3

Abstract

Given a coarse space (X,E)(X, \mathcal{E}) with the bornology B\mathcal B of bounded subsets, we extend the coarse structure E\mathcal E from X×XX\times X to the natural coarse structure on (B\{})×(B\{})(\mathcal B \backslash \lbrace \emptyset\rbrace)\times (\mathcal B \backslash \lbrace \emptyset\rbrace) and say that a macro-uniform mapping f:(B\{})Xf: (\mathcal B \backslash \lbrace \emptyset\rbrace)\rightarrow X (resp. f:[X]2Xf: [ X]^2 \rightarrow X) is a selector (resp. 2-selector) of (X,E)(X, \mathcal{E}) if f(A)Af(A)\in A for each AB{}A\in \mathcal B\setminus \lbrace\emptyset\rbrace (resp. A[X]2)A \in [X]^2 ). We prove that a discrete coarse space (X,E)(X, \mathcal{E}) admits a selector if and only if (X,E)(X, \mathcal{E}) admits a 2-selector if and only if there exists a linear order \leq on XX such that the family of intervals {[a,b]:a,bX, ab}\lbrace [a, b]: a,b\in X, \ a\leq b \} is a base for the bornology B\mathcal B.

Keywords

Cite

@article{arxiv.2101.07199,
  title  = {Selectors of discrete coarse spaces},
  author = {Igor Protasov},
  journal= {arXiv preprint arXiv:2101.07199},
  year   = {2021}
}

Comments

bornology, coarse space, selector