is a partially solved Sudoku, using easy and medium difficulty solving techniques; no more squares can be solved using them.

InNovember 2006, The Times introduced a new extreme level of Sudoku giving players a moredifficult level of logic: Super Fiendish.With many advanced techniques, the key is to spot patterns within your pencil marks to eliminate possibilities within other squares. Pencil marks are small numbers, usually written at the top of each unsolved square, listing all the possible values for that square. The goal is to fill the grid, so that each row, column, and 3x3 block contain all the digits from 1 to 9 without repeating. So, as we increase the difficulty Super Fiendish, the time has come to present the essential techniques for solving the most difficult Sudoku puzzles.

Well, you have established that the 7 for the first column must be in one of the two highlighted rows; not in any other squares in this column. Essentially, this method uses the fact that in certain cases, there are only two possible ways of placing two numbers in four squares which form a rectangle.

To print the puzzles use either the Print button below the grid, or if you want to print the pencilmarks as well, use the browser Print option under the File menu.