topo.removeVertex(src.getNode());
}
if (topo.containsVertex(dst.getNode())
&& topo.inDegree(dst.getNode()) == 0
&& topo.outDegree(dst.getNode()) == 0) {
topo.removeVertex(src.getNode());
}
if (topo.containsVertex(dst.getNode())
&& topo.inDegree(dst.getNode()) == 0
&& topo.outDegree(dst.getNode()) == 0) {