sS arbitraryVarsToStars(Set<S> vars, S s, LS varNames_out) {
  if (empty(vars)) ret s;
  L<S> tok = javaTok(s);
  for (int i = 1; i < l(tok); i += 2) {
    S t = tok.get(i);
    if (vars.contains(t)) {
      listAdd(varNames_out, t);
      tok.set(i, "*");
    } else if (eq(t, "*"))
      listAdd(varNames_out, "*");
  }
  ret join(tok);
}