Applications of foldings of A-graphs
This thesis gives some applications of the theory of folding of A-graphs. In the first application, we investigate the relationship between the bridge number of a knot k, a geometrically defined invariant of the knot, and the meridional rank of the knot group G(k). We give a new proof that these two invariants coincide if k is a torus knot. With similar techniques we show that the same holds if k is a knot whose complement is a graph manifold. Next, we study killers of knot groups. We prove that the group G(k) of any cable knot k contains infinitely many killers, none of which is the automorphic image of another. As a corollary we show that if k is a knot whose complement is a graph manifold, then G(k) has the same property. Finally, we study generating sets of planar discontinuous groups. We show for a large class of planar discontinuous groups that there are only finitely many Nielsen equivalence classes of generating tuples.