static TreeSet<Symbol> litsymbolset(S... items) {
  TreeSet<Symbol> set = symbolSet();
  for (S a : items) set.add(symbol(a));
  ret set;
}

ifclass Symbol
static TreeSet<Symbol> litsymbolset(Symbol... items) {
  TreeSet<Symbol> set = symbolSet();
  for (Symbol a : items) set.add(a);
  ret set;
}
endif