The word problem for G is the set of words on X which represent the identity element of G . Indeed, G has a regular word problem if and only if it is finite, and a context free word problem if and only if it is virtually free. It is also possible to classify word hyperbolic groups in this manner. In a different direction, one can define a notion of regularity for subsets of word hyperbolic groups. The problem of computing the Gersten-Stallings angle between subgroups of a hyperbolic group can often be reduced to the membership problem of a certain regular subset.
B are quasiconvex.
Then the angle between A and B is computible. I will attempt to define as many of the above concepts as possible. For example, word hyperbolic groups, regular languages, context free languages, the Gersten-Stallings angle, etc., will all be defined. Heinz-Juergen Voss , of the Technical University of Dresden . Light subgraphs of multigraphs embedded in compact 2-manifolds.