Speaker: Bruce Richter, Dept. of Combinatorics and Optimization, 
         University of Waterloo
Time:    Thursday, September 5th, 1:30 p.m.
Place:   Macphail room, HP4351, School of Math and Stats, Carleton University
Title:   What is the cycle space of an infinite graph?

Abstract:  There have been three main lines recently developing the notion
of cycle space of an infinite graph.  Bonnington and Richter have
generalized to locally finite graphs the fact that the face boundaries of
a planar map generate the cycle space.  In this case, the cycle space
consists of all (edge-sets of) subgraphs in which every vertex has even
degree.  Diestel and Kuhn have considered when the fundamental cycles of a
spanning tree generate the cycle space.  In this case,the cycle space
consists of all (restricted infinite) sums of circuits, which include
2-way infinite paths having the same "end point".  Finally, Bruhn has
generalized to countable graphs having one end Tutte's theorem that
the "peripheral cycles" of a 3-connected graph generate the cycle space.
In this case, the cycle space consists of finite sums of circuits.
The purpose of this talk is to give an overview of these results and to
discuss a point of view from which these might be unified.