Normal sudoku rules apply. The grid is covered in fog. Placing a correct digit in a cell lifts fog in that cell and possibly other cells; revealing new clues. On an “index line”, the digit in the Nth cell along the line (starting from the diamond) indicates the position along the line where the digit N appears. For example: 3214 would be a valid line with the 3 on the diamond; the 1st digit, 3, indicates that the 3rd digit is a 1, and so on. Inequality signs point to the smaller of the two digits. Digits separated by a white dot are consecutive. Digits separated by an X sum to 10. Not all such symbols are necessarily given.