Divide the grid into eight non-overlapping 2x4 regions, which can each be placed either horizontally or vertically. It must be determined which one of the digits 1-9 is missing from the grid. The other eight digits should each appear once in every row, column and region. RENBAN (pink) - digits along the pink line form a non-repeating consecutive set, which can appear in any order. NABNER (yellow) - no two digits on the yellow line may be consecutive (or the same.) REGION SUM (darker blue) - on the blue line, digits in each region have the same total. GERMAN WHISPER (green) - adjacent digits on the green line must have a difference of at least 5. PARITY (red) - digits on the red line must alternate between odd and even. PALINDROME (grey) - the string of digits on the grey line reads the same in either direction. SAME DIFFERENCE (turquoise) - each pair of adjacent digits on a turquoise line has the same difference. This difference value can be different for different turquoise lines. KROPKI - two digits connected by a black dot have a 2:1 ratio (ie one is double the other.)