Normal sudoku rules apply. The two puzzles must be solved in tandem. The puzzles overlap at the Loop in R9C9 (so eg. R9C7 in North Side and R1C6 in South Side contain the same digit). All cells with an airplane contain the same digit across both puzzles. Red Line: Parity line (cells alternate in parity). Purple Line: Zipper line (digits an equal distance from the center sum to the digit in the center). Yellow Line: Nabner line (no two digits can be consecutive or identical). Blue Line: Region Sum line (box borders divide the line into segments with an equal sum). Green Line: German Whisper line (adjacent digits differ by 5 or more). Orange Line: Dutch Whisper line (adjacent digits differ by 4 or more). Brown Line: Slow thermo (moving from the bulb, each digit is the same or higher). Pink Line: Renban line (a set of consecutive digits in any order).