if (!inList.contains(e)) {
            inList.add(e);
        }

        return this;
    }
    // ------------------------------------------------------------------------
    public MetadataGraph removeVertex(MetadataGraphVertex v) {
        if (vertices != null && v != null) {
            vertices.remove(v);
        }

        if (incidentEdges != null) {
            incidentEdges.remove(v);
        }