private bool IsLinkToBeRemoved(Link link, HashSet<Link> sellinks, IDataCollection sel) { // only called when not ILinksModel
if (link == null) return false;
if (sellinks.Contains(link)) return false;
if (link.CachedParentSubGraph != null && sel.ContainsNode(link.CachedParentSubGraph.Data)) return false;
return true;
}