sS firstUnusedCountingDollarVar(S text) {
  L<S> tok = javaTok(text);
  Set<S> usedVars = allDollarVarsInText(tok);
  for (int i = 1; ; i++) {
    S var = "$" + i;
    if (!usedVars.contains(var))
      ret var;
  }
}