static LineCompReader lcMerge(LineCompReader lc1, LineCompReader lc2) {
  LCMerge merger = new(lc1, lc2);
  merger.run();
  ret merger.lcOut;
}

srecord noeq LCMerge(LineCompReader lc1, LineCompReader lc2) {
  new LineCompReader lcOut;
  Map<IntPair, Int> pairIndex;
  Map<Char, Int> literalIndex;
  new Map<Int> lc2map;
  int newLiterals; // number of literals added compared to lc1
  int newPairs;

  run {
    pairIndex = indexList(lc1.pairs);
    literalIndex = indexList(lc1.literals);
  
    // make lcOut.literals & literalIndex
  
    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 == null) {
        iLit = addAndReturnIndex(lcOut.literals, c);
        literalIndex.put(c, iLit);
      }
      lc2map.put(i, iLit);
    }
    
    newLiterals = l(lcOut.literals)-l(lc1.literals);
    
    // clone lc1.pairs into lcOut.pairs, add lc2.pairs
    
    new Map<Int> map2;
    lcOut.pairs = map(lc1.pairs, p -> intPair(adjust1(p.a), adjust1(p.b)));
    
    for (int i = 0; i < l(lc2.pairs); i++) {
      IntPair p = lc2.pairs.get(i);
      Int iPair = pairIndex.get(p);
      if (iPair == null) { // new pair
        iPair = addAndReturnIndex(lcOut.pairs, p);
        pairIndex.put(p, iPair);
      }
      lc2map.put(l(lc2.literals)+i, l(lcOut.literals)+iPair);
    }
    
    newPairs = l(lcOut.pairs)-l(lc1.pairs);
  }
  
  int adjust1(int i) {
    ret i >= l(lc1.literals) ? i+newLiterals : i;
  }
}