Latin Square rules apply (ie place the digits 1-9, once each, into every row and column). The grid is covered in a checkerboard pattern of yellow and blue cells. Each digit appears in one of the colours exactly as many times as its value. For example, 7 will appear either exactly seven times in blue or exactly seven times in yellow. Digits may not repeat along any negative diagonal (those going from the top left to the bottom right). Cells separated by a single knightâs move (in chess) cannot contain the same digit. Digits in grey circles must be odd.