function undirEdgeId(u, v) {
    return u < v
      ? u.toString().length + ':' + u + '-' + v
      : v.toString().length + ':' + v + '-' + u;
  }
function undirEdgeId(u, v) {
    return u < v
      ? u.toString().length + ':' + u + '-' + v
      : v.toString().length + ':' + v + '-' + u;
  }
function undirEdgeId ( u , v ) { return u < v ? u . toString ( ) . length + ':' + u + '-' + v : v . toString ( ) . length + ':' + v + '-' + u ; }
/*
Generate an ID that can be used to represent any undirected edge that is
incident on `u` and `v`.
/ * Generate an ID that can be used to represent any undirected edge that is incident on u and v .