Normal sudoku rules apply. A letter indicates the same whole number whenever it appears (eg the letter B could represent the number 10 throughout the puzzle); and each letter represents a different number. Digits in a cage sum to the total in the cage’s upper left corner. Red numbers outside the grid indicate the sum of all digits along the indicated diagonal. Black numbers outside the grid indicate the sum of the first N digits in that row or column (counting from the direction of the clue), where N is the digit in the first cell in that row or column (closest to the clue.)