(*os) << " node [shape=circle,width=0.75,fixedsize=true];" << endl;
(*os) << " edge [color=gray,arrowhead=open]" << endl;
(*os) << " " << _source->id << " [peripheries=2];" << endl;
(*os) << " node [shape=circle,width=0.75,fixedsize=true];" << endl;
(*os) << " edge [color=gray,arrowhead=open]" << endl;
(*os) << " " << _source->id << " [peripheries=2];" << endl;