Normal sudoku rules apply. Enter correct digits to clear fog. No guessing is necessary. In every row, column and box, there is exactly one 'pseudo cell'. The digits 1-9 each appear once in a pseudo cell. The real value of a pseudo cell is calculated by adding its row number to its column number. Eg: if there is a pseudo cell in r8c5, it has the value of 13, regardless of which digit is in that cell. On a lavender 'zipper' line, the values of any pair of cells that are an equal distance from the central spot always sum to the value on that central spot. On a turquoise 'same difference' line, the values of adjacent cells always have the same difference (but this difference may be different for different turquoise lines.) Values joined by a V sum to 5.