Normal sudoku rules apply. Cells separated by one move of a chess knight may not contain the same digit. For each line, the digits in the two cells marked with dots are ‘look-and-say clues’ ie in at least one way of reading them, one digit indicates how many times the other digit appears on the line. (eg if the marked cells contain 78 it can mean the line has seven instances of 8, or eight instances of 7). Adjacent digits along an orange line must have a difference of at least 4.