Menger's and Hurewicz's Problems: Solutions from "The Book" and refinements

Details Menger's and Hurewicz's Problems: Solutions from "The Book" and refinements Menger's and Hurewicz's Problems: Solutions from "The Book" and refinements

2009-09-30

arxiv.org/abs/0909.5645v4

Mathematics

General Topology

Corrected a typo detected by Ivan Khatchatourian

Scientific paper

We provide simplified solutions of Menger's and Hurewicz's problems and conjectures, concerning generalizations of sigma-compactness. The reader who is new to this field will find a self-contained treatment in Sections 1, 2, and 5. Sections 3 and 4 contain new results, based on the mentioned simplified solutions. The main new result is that there is a set of reals X of cardinality equal to the unbounding number b, and which has the following property: "Given point-cofinite covers U_1,U_2,... of X, there are for each n sets u_n,v_n in U_n, such that each member of X is contained in all but finitely many of the sets u_1 union v_1,u_2 union v_2,..." This property is strictly stronger than Hurewicz's covering property, and by a result of Miller and the present author, one cannot prove the same result if we are only allowed to pick one set from each U_n.

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