public override string ToString()
{
return "Edge " + _edgeIndex + "; sites " + _sites[LR.LEFT] + ", " + _sites[LR.RIGHT]
+ "; endVertices " + (_leftVertex != null ? _leftVertex.VertexIndex.ToString() : "null") + ", "
+ (_rightVertex != null ? _rightVertex.VertexIndex.ToString() : "null") + "::";
}