static LS ai_turnCertainWordsIntoUniqueDollarVars(Set<S> wordsToTransform, LS tok) {
  MultiSet<S> ms = ciMultiSet();
  ret mapWithIndex(tok, (i, t) ->
    odd(i) && contains(wordsToTransform, t) ? "$" + t + addPrefixIfNempty("_", emptyIfOne(ms.add(t))) : t);
}

sS ai_turnCertainWordsIntoUniqueDollarVars(Set<S> wordsToTransform, S s) {
  ret join(ai_turnCertainWordsIntoUniqueDollarVars(wordsToTransform, javaTok(s)));
}