@Nullable
    private Pair<Integer, Side> transferOffsetToTwoside(int offset) {
      LineCol onesidePosition = LineCol.fromOffset(myDocument, offset);

      Pair<int[], Side> pair = transferLineFromOneside(onesidePosition.line);
      Side side = pair.second;
      int twosideLine = side.select(pair.first);
      if (twosideLine == -1) return null;

      Document twosideDocument = getDocument(side);
      LineCol twosidePosition = new LineCol(twosideLine, onesidePosition.column);
      return Pair.create(twosidePosition.toOffset(twosideDocument), side);
    }
@Nullable
    private Pair<Integer, Side> transferOffsetToTwoside(int offset)