docs: public void makeReferences(CellRow row, CellCol col, CellSqr sqr) {
          this.cellRow = row;
          this.cellCol = col;
          this.cellSqr = sqr;
          this.exCells = new HashSet<Cell>();
          this.exCells.addAll(this.cellRow.getCells());
          this.exCells.addAll(this.cellCol.getCells());
          this.exCells.addAll(this.cellSqr.getCells());
          this.exCells.remove(this);
      }