sS combineToDollarVarPattern(S a, S b) {
  L<S> tok1 = codeTokens(dropPunctuation(javaTok(a)));
  L<S> tok2 = codeTokens(dropPunctuation(javaTok(b)));
  if (l(tok1) != l(tok2)) null;
  new L<S> out;
  Iterator<S> varNames = allWordsOfAlphabet(lowerCaseAlphabet());
  varNames.next(); // Skip "$"
  for i over tok1: {
    S t = tok1.get(i);
    out.add(eq(t, tok2.get(i)) ? t : "$" + varNames.next());
  }
  ret joinWithSpace(out);
}