Normal sudoku rules apply. Most of the grid is obscured by fog. Placing a correct digit will remove the fog surrounding that cell. Each letter from A-J uniquely represents one of the digits 0-9. A two-letter clue represents a two-digit number which does not begin with 0. A clue outside the grid represents the sum of the digits in the first X cells seen from that clue, where X is the first cell seen. (Eg if r1c5 is a 5 then the IF clue is summing the first 5 cells in its column.) Digits in a cage do not repeat and sum to the cage total, which is given in the leftmost cell of the highest row of the cage.