Normal sudoku rules apply. Colour the grid using two colours, such that all cells of the same colour are orthogonally connected, and no 2x2 area is fully one colour. Odd clues outside the grid give the first odd digit seen from that direction; even clues give the first even digit seen from that direction. Each such odd or even clue is a single digit and only sees digits of one yin yang colour, while digits of the other colour are completely meaningless for that clue. Which colour corresponds to each clue must be determined. Some clues are covered in fog. Placing correct digits in the grid may lift some of the fog to reveal more clues.