Forthcoming events in this series


Wed, 28 Apr 2010
11:30
L3

tba

Ivan Reilly
(Auckland)
Thu, 23 Jul 2009
11:30
L3

Shadowing, entropy and a homeomorphism of the pseudoarc.

Piotr Oprocha
((Murcia and Krakow))
Abstract

In this talk we present a method of construction of continuous map f from [0, 1] to itself, such that f is topologically mixing, has the shadowing property and the inverse limit of copies of [0, 1] with f as the bounding map is the pseudoarc. This map indeuces a homeomorphism of the pseudoarc with the shadowing property and positive topological entropy. We therefore answer, in the affirmative, a question posed by Chen and Li in 1993 whether such a homeomorphism exists.

Wed, 21 Jan 2009
16:00
L3

TBA

TBA
Mon, 12 Jan 2009
14:00
L3

Zermelo set theory, Mac Lane set theory and set forcing

Adrian Mathias
(Reunion)
Abstract

Over certain transitive models of Z, the usual treatment of forcing goes awry. But the provident closure of any such set is a provident model of Z, over which, as shown in "Provident sets and rudimentary set forcing", forcing works well. In "The Strength of Mac Lane Set Theory" a process is described of passing from a transitive model of Z + Tco to what is here called its lune, which is a larger model of Z + KP.

Theorem: Over a provident model of Z, the two operations of forming lunes and generic extensions commute.

Corresponding results hold for transitive models of Mac Lane set theory + Tco.

Wed, 19 Nov 2008
16:00
L3

TBA

James Vicary
(Comlab)
Wed, 12 Nov 2008
16:00
L3

'Two-point sets and the Axiom of Choice'.

Ben Chad
(Oxford)
Abstract

'A two-point set is a subset of the plane which meets every line in exactly two points. The existence of two-point sets was shown by Mazurkiewicz in 1914, and the main open problem concerning these objects is to determine if there exist Borel two-point sets. If this question has a positive answer, then we most likely need to be able to construct a two-point set without making use of a well-ordering of the real line, as is currently the usual technique.

We discuss recent work by Robin Knight, Rolf Suabedissen and the speaker, and (independently) by Arnold Miller, which show that it is consistent with ZF that the real line cannot be well-ordered and also that two-point sets exist.'