/// <summary>
/// Returns the markers that have annotated a given vertex
/// </summary>
/// <param name="vertex">The vertex in question</param>
/// <returns>The set of markers that have annotated this vertex</returns>
public virtual Set GetAnnotationMarkers(object vertex)
{
DefaultSet set = new DefaultSet();
foreach (Pair <int, object> p in annotations.GetValues(vertex))
{
set.Add(p.Object1);
}
return(set);
}