static LineCompReader lcMerge(LineCompReader lc1, LineCompReader lc2) {
  Map<IntPair, Int> pairIndex = indexList(lc1.pairs);
  Map<Char, Int> literalIndex = indexList(lc1.literals);
  new LineCompReader lcOut;
  
  // process literals
  
  lcOut.literals = cloneList(lc1.literals);
  for (int i = 0; i < l(lc2.literals); i++) {
    char c = lc2.literals.get(i);
    Int iLit = literalIndex.get(c);
    if (iLit == 0)
      literalIndex.put(c, addAndReturnIndex(lcOut.literals, c));
  }
  
  ret lcOut;
}