Examples of non-shy sets
Fundamenta Mathematicae, Tome 144 (1994) no. 1, pp. 73-88
Christensen has defined a generalization of the property of being of Haar measure zero to subsets of (abelian) Polish groups which need not be locally compact; a recent paper of Hunt, Sauer, and Yorke defines the same property for Borel subsets of linear spaces, and gives a number of examples and applications. The latter authors use the term "shyness" for this property, and "prevalence" for the complementary property. In the present paper, we construct a number of examples of non-shy Borel sets in various groups, and thereby answer several questions of Christensen and Mycielski. The main results are: in many (most?) non-locally-compact Polish groups, the ideal of shy sets does not satisfy the countable chain condition (i.e., there exist uncountably many disjoint non-shy Borel sets); in function spaces $C(^ω 2,G)$ where G is an abelian Polish group, the set of functions f which are highly non-injective is non-shy, and even prevalent if G is locally compact.
@article{10_4064_fm_144_1_73_88,
author = {Randall Dougherty},
title = {Examples of non-shy sets},
journal = {Fundamenta Mathematicae},
pages = {73--88},
year = {1994},
volume = {144},
number = {1},
doi = {10.4064/fm-144-1-73-88},
language = {en},
url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-144-1-73-88/}
}
Randall Dougherty. Examples of non-shy sets. Fundamenta Mathematicae, Tome 144 (1994) no. 1, pp. 73-88. doi: 10.4064/fm-144-1-73-88
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