Normal sudoku rules apply. Digits in cages cannot repeat and must sum to the small clue in the top left corner of the cage. Digits an equal distance from the centre of a blue zipper line must sum to the same total. For odd length lines, the total is the digit in the centre of the line. The grey line is a palindrome and must read the same forwards and backwards. A digit on any line also indicates how many times that digit appears on all lines in the puzzle.