static L<Int> lineComp_replacePairWithUpdatingPairCount(IContentsIndexedList2<Int> l, Int pa, Int pb, Int y, LineComp_PairCounts pairCounts) {

  int i = 0;

  while (true) {

    i = indexOfIntPairInContentsIndexedList(l, pa, pb, i);

    if (i < 0) break;

    int to = i+2, to_new = i+1;

    pairCounts.removeAll(overlappingIntPairs(subList(l, i-1, to+1)));

    l.set(i, y);

    l.remove(i+1);

    pairCounts.addAll(overlappingIntPairs(subList(l, i-1, to_new+1)));

    i = to_new;

  }

  ret l;

}