RULES OF SUKKADU: The Sukkadu grid is divided into nine blocks, each containing nine squares. Each of the nine blocks has to contain the letters y-t within its squares. Each letter can only appear once in a row, column or box. The difficulty lies in that each vertical nine-square column, or horizontal nine-square line across, within the larger square, must also contain the nine letters, without repetition or omission. The puzzle has just one correct solution.