Normal sudoku rules apply. The grid 'wraps around' (the top connects to the bottom, and the left edge to the right edge). DUTCH CELLMATES: Every digit in the grid needs to have a digit at least 4 greater in the cell below it, or a digit at least 4 smaller in the cell above it. It may have both, but doesn't need both. KILLER CAGES: Cages chained to each other have the same sum.