Normal sudoku rules apply. "V" can be either "inequality" (arrow ‘points’ to smaller digit) or "two digits sum to 5" or both. If the two digits do sum to 5, the "V" can be in any orientation and does not necessarily indicate ‘greater than/less than’. Digits must not repeat in cells that are a chess knight's move apart. The digits in a cage must sum to the number printed in its corner. Entering a correct digit will clear the fog from around that cell.