// returns (text, map of number -> var)
static Pair<S, SS> replaceNumbersWithABCDollarVars(S s) {
  Set<S> taken = asHashSet(regexpExtractAllIC("\\$[a-z]+", s));
  ret replaceNumbersWithVars_returnMap(s, abcDollarVarMakerWithoutTaken(taken));
}