Using the same logic in the last column, you can also eliminate the 7 as a possibility from all squares which are not in either highlighted row (Fig. 2). The pivot contains candidates XY. The pincers - candidates XZ and YZ. Any cell that intersects both pincers can’t longer contain a candidate for digit Z, because the pivot means either of the pincers to contain this digit. Why play Evil Sudoku? Pencil marks are small numbers, usually written at the top of each unsolved square, listing all the possible values for that square. In Fig. 4, the relevant pencil marks are entered to show that you have two possible squares in which the 3 can be placed in the third and fourth columns, and three possible squares in the seventh column (highlighted).

So, there are two possible ways of placing the 7; how does this help you solve anything? 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. If you like playing some seriously hard Sudoku, try the puzzles at the end of The Times Sudoku 6 book with some requiring the swordfish technique. Solving these puzzles is a different matter entirely, since these are the most difficult puzzles we create. Difficulty depends on the type of steps required to solve them, and also on the number of each type of step. See our guide to solution rules for hard sudoku puzzles. First a couple of preliminary points: if you have ever completed any Fiendish or Super Fiendish Sudoku, you will be familiar with noting down candidates or pencil marks.To give you a good chance of spotting the swordfish you should enter all the pencil marks in the grid as shown here. InNovember 2006, The Times introduced a new extreme level of Sudoku giving players a moredifficult level of logic: Super Fiendish.

If you really like Super Fiendish, you will have to wait a little longer for The Times Sudoku 7 with 25 extremely hard Sudoku, many requiring x-wing or swordfish to complete. So, as we increase the difficulty Super Fiendish, the time has come to present the essential techniques for solving the most difficult Sudoku puzzles. Look along each of the rows in turn, noting each one that contains only two or three squares with the current number as a possibility. A swordfish is found when for three rows, there are two or three possible squares in which a particular number can be placed, and for all three rows these squares lie in the same three columns.While it's totally fine to play sudoku intuitively on the easy levels, evil sudoku requires the knowledge of some strategies. Here is the most popular one for solving sudoku on the evil level. The swordfish technique isnamed aftera World War II biplane called the “Fairey Swordfish”, a Torpedo Spotter Reconnaissance biplane used by the Royal Navy from 1936 to 1945.