static void web_copyRelations(WebNode src, WebNode dest) {
  if (src == dest) ret;
  Web web = src.web;
  assertSame(web, dest.web);
  
  for (Pair<WebNode> p : cloneList(keys(web.relations))) {
    if (p.a == src)
      web.getRelation(dest, p.b).addLabels(web.getRelation(p).labels);
    if (p.b == src)
      web.getRelation(p.a, dest).addLabels(web.getRelation(p).labels);
  }
}

Began life as a copy of #1009837