2 new papers this month, from Biss-Farb and Flores. 

                  Mark Hovey

New papers appearing on hopf between 5/4/04 and 6/2/04

1.
http://hopf.math.purdue.edu/cgi-bin/generate?/Biss-Farb/kg


Title:  K_g is not finitely generated
Authors:  Daniel Biss and Benson Farb
Author's email addresses:  daniel@math.uchicago.edu, farb@math.uchicago.edu 
Included files:  curve1.eps and curve3.eps

Abstract:  We prove that for any genus g>1, the subgroup K_g of the
mapping class group of a closed genus g surface generated by Dehn
twists about separating curves is not finitely generated.

2.
http://hopf.math.purdue.edu/cgi-bin/generate?/Flores/draft2

Nullification functors and the homotopy type of the classifying space
for proper bundles

Ram'on J. Flores

Departamento de Matem'aticas,
Universidad Aut'onoma de Barcelona,
E-08193 Bellaterra,
Spain

E-mail address: ramonj@mat.uab.es

 Abstract. Let G be a discrete group. In this note we build a bridge
 between the homotopy theory of BG and the theory of proper G-actions,
 by showing that under mild restrictions, the classifying space for
 proper G-bundles has the homotopy type of the W-nullification of BG for
 some space W. This allows us to use properties of the localization
 functors to obtain spaces that are homotopy equivalent to this "proper"
 classifying space for a wide range of groups, and on the other hand, we
 take profit of the existence of well-known geometrical and
 finite-dimensional models of it for some infinite groups to deduce
 homotopical information about the p-primary part of their classifying
 spaces.

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