static public LookupBackedSet <KEY_TYPE, VALUE_TYPE> AppendFallbacks <KEY_TYPE, VALUE_TYPE>(this LookupBackedSet <KEY_TYPE, VALUE_TYPE> item, IEnumerable <LookupSet <KEY_TYPE, VALUE_TYPE> > fallbacks)
{
return(new BackedSet <KEY_TYPE, VALUE_TYPE>(item.GetMainSet(), item.GetFallbackSets().Append(fallbacks)));
}