// returns func(S) -> S or fails
// returnFullText = false: return only answer
static O ai_relateTwoTokens(S text1, S text2, L functionsToTry, bool returnFullText) {
  L<S> t1 = javaTok(text1), t2 = javaTok(text2);
  if (l(t1) != l(t2)) quickFail();
  L<Triple<S, S, Int>> diffs = differencesElementByElement_codeTokensOnly(t1, t2);
  if (l(diffs) != 2) quickFail();
  Triple<S, S, Int> d1 = first(diffs), d2 = second(diffs);
  for (O f : functionsToUse) {
    if (checkFunctionOnPairs(f, ll(pair(d1.a, d2.a), pair(d1.b, d2.b))))
      ret ai_relateTwoTokens_solver(t1, d1.c, d2.c, f, returnFullText);
    if (checkFunctionOnPairs(f, ll(pair(d2.a, d1.a), pair(d2.b, d1.b))))
      ret ai_relateTwoTokens_solver(t1, d2.c, d1.c, f, returnFullText);
  }
  throw quickFail("No function found");
}

static O ai_relateTwoTokens_solver(final L<S> answerTmpl, final int i, final int j, fO f, final bool returnFullText) {
  ret func(S s) {
    L<S> tok = javaTok(s);
    int l = l(tok);
    tok.addAll(subList(answerTmpl, l));
    tok.set(j, (S) callF(f, tok.get(i)));
    ret returnFullText ? join(tok) : join(subList(tok, l-1));
  };
}