P. Elbau, G.M. Graf
Equality of bulk and edge Hall conductance revisited
(59K, LaTeX with 1 .pstex/.pstex_t figure)

ABSTRACT.  The integral quantum Hall effect can be explained either as resulting from 
bulk or edge currents (or, as it occurs in real samples, as a combination of 
both). This leads to different definitions of Hall conductance, which agree 
under appropriate hypotheses, as shown by Schulz-Baldes et al. by means of 
$K$-theory. We propose an alternative proof based on a generalization of the 
index of a pair of projections to more general operators. The equality of 
conductances is an expression of the stability of that index as a flux tube 
is moved from within the bulk across the boundary of a sample.