/// <summary>
/// Returns a new set that contains the new elements and the old elements.
/// </summary>
public OrderedSet <T> Union(IEnumerable <T> new_elems)
{
var set = new OrderedSet <T>(this, count);
set.AddRange(new_elems);
return(set);
}
/// <summary>
/// Returns a new set that contains the new elements and the old elements.
/// </summary>
public OrderedSet <T> Union(params T[] new_elems)
{
var set = new OrderedSet <T>(this, count);
set.AddRange(new_elems);
return(set);
}