  The infrared behaviour of vertex functions in an SU(N) Yang-Mills theory in
Landau gauge is investigated employing a skeleton expansion of the
Dyson-Schwinger equations. The three- and four-gluon vertices become singular
if and only if all external momenta vanish while the dressing of the
ghost-gluon vertex remains finite in this limit. The running coupling as
extracted from either of these vertex functions possesses an infrared fixed
point. In general, diagrams including ghost-loops dominate in the infrared over
purely gluonic ones.
