Normal sudoku rules apply. Battlefield: Consider the first X cells and the last Y cells of each row and column, where X is the number in the first cell and Y is the number in the last cell. These groups of cells will either overlap or leave a gap. Clues outside the grid give the sum of the cells in the resulting gap or overlap. ALL cells that are part of an overlap in BOTH their row and column are red. ALL cells that are part of a gap in BOTH their row and column are green.