  If X is a proper CAT(-1)-space and $\Gamma$ a non-elementary discrete group
of isometries acting properly discontinuously on X, it is shown that the
geodesic flow on the quotient space Y=X/$\Gamma$ is topologically mixing,
provided that the generalized Busemann function has zeros on the boundary
$\partial X$ and the non-wandering set of the flow equals the whole quotient
space of geodesics GY:=GX/$\Gamma$ (the latter being redundant when Y is
compact). Applications include the proof of topological mixing for (A) compact
negatively curved polyhedra, (B) compact quotients of proper geodesically
complete CAT(-1)-spaces by a one-ended group of isometries and (C) finite
n-dimensional ideal polyhedra.
