X-Sudokus (or Samurai Sudokus) are an extension to the massively popular sudoku puzzles, just taken a little bit further. X-Sudokus consist of five normal sudoku puzzles, arranged like the five on a domino (to form a rough "X" shape) with the outer four puzzles overlapping one box with the central grid.
As with sudokus, the idea behind the puzzles is that each of the squares should contain a number from 1 to 9. There are just three restrictions:
With X-Sudoku puzzles, it's made a bit trickier with the five overlapping grids, but essentially all the same rules apply.
On the right is a picture of an example puzzle (Puzzle 1). Each of the outer sudokus shares one 9-by-9 box with the central sudoku.
The basic techniques are just the same as in normal sudokus, but the same rules get a little bit more complicated in the overlaps between the grids. The techniques for single sudokus are outlined in the sudoku tutorial including simple examples.
As part of the Activity Workshop, the applet game for Sudokus one has been extended to cope with five grids at once. You can have a go of the puzzles yourself in the browser, and the game will warn you if you've gone wrong. It also lets you undo your moves easily and gives visual highlighting clues. See the page about the Sudoku helper for instructions.
There are two puzzles to try out, starting with Puzzle 1. Enjoy!