lib/natural/util/topological.js
function(g) {
    this.isDag = true;
    this.sorted = topoSort(uniqueVertexs(g.edges()), g.edges());
}
function(g) {
    this.isDag = true;
    this.sorted = topoSort(uniqueVertexs(g.edges()), g.edges());
}
function ( g ) { this . isDag = true ; this . sorted = topoSort ( uniqueVertexs ( g . edges ( ) ) , g . edges ( ) ) ; }
a topo sort for a digraph
@param {Digraph}
a topo sort for a digraph