Normal sudoku rules apply. The grid is covered with fog, with an initial light source in the centre cell. Digits also act as light sources and, when placed correctly, illuminate the cells around them. The sum of the digits within a cage is given in the left-most cell of the top row reached by the cage (all cage sums are given). Digits cannot repeat within a cage. Digits on arrows sum to the number in the connected circle, and can repeat if allowed by other rules. All arrow sums are single-digit, and arrows do not overlap or intersect. Digits in cells with a grey circle must be odd. Digits in cells with a grey square must be even. Cells separated by a knight's move (in chess) cannot contain the same digit.