/// <summary>
/// Gets the <see cref="IVertex"/> parent.
/// </summary>
/// <param name="v">current vertex</param>
/// <returns>
/// parent vertex if any, null reference otherwize
/// </returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="v"/> is a null reference
/// </exception>
/// <exception cref="MultipleInEdgeException">
/// <paramref name="v"/> has multiple in-edges
/// </exception>
public IVertex ParentVertex(IVertex v)
{
if (v == null)
{
throw new ArgumentNullException("v");
}
if (this.Wrapped.InDegree(v) > 1)
{
throw new MultipleInEdgeException(v.ID.ToString());
}
return(Traversal.FirstSourceVertex(this.Wrapped.InEdges(v)));
}