How to play You can also type the starting numbers in from another source, e.g. a puzzle in a book or newspaper. Follow the instructions in the righthand column for typing in your own numbers. To solve the puzzle, type numbers into the empty squares so that each horizontal row and vertical column contains the numbers 1 to 9 (i.e. with no numbers repeated). The difficult bit is that each 9square rectangle (the areas surrounded by darker lines) must also contain the numbers 1 to 9, with no repetitions. To see an example of a completed puzzle, press 'Solve Puzzle'. If 'Show errors' is checked and you type an incorrect number, it will be
shown in red (note  this only works with singlesolution puzzles). Using candidate lists. A key technique in sudkou solving is writing the candidate (possible) numbers for each empty square in the corner of the square. You can do this in this page, by clicking in the topleft corner and typing the numbers in. In manual mode it's up to you to maintain these lists, just like a printed
puzzle. In automatic mode, the page calculates the lists for you, updating them
whenever you solve a square. That's not 'proper' solving, of course, but is
useful for practising pattern recognition. Random Puzzle. Generates a singlesolution puzzle with a symmetrical layout. You can choose from 36 down to 22 starting squares. The difficulty rating of a puzzle is unknown until it's been generated, but choosing fewer squares will tend to create harder puzzles. This version has a new generator for puzzles with 30 or more starting squares. 30square puzzles now range from 'easy' to outlaw rating, and are produced very quickly (mostly!). Gallery Puzzle. This gets a prebuilt puzzle (singlesolution, symmetrical) from the Gallery, with your choice of difficulty level. Click 'see all' to view the Gallery menu, and choose a puzzle to solve. Nonsymmetric puzzle. This generates a singlesolution puzzle with your choice of difficulty level. The layout will be nonsymmetrical. To be solvable entirely by logic (no guesses), a puzzle must have only one possible solution. All puzzles generated by this page (including Gallery puzls) are singlesolution. The page will warn you if a puzzle you've typed in or imported has more than one solution. Please note  puzzles rated 'outlaw' by this page may still require a guess, even though they have just one solution. All other puzzles generated by this page's 'Random Puzzle' button are guaranteed to be solvable by logic alone. Have fun! 
Tip: Use Firefox to view the solver  it shows the numbers as they're
being calculated.
Tip #2: Press Tab after you type each number (or just click somewhere else on the page)  this will check your data, and update auto candidate lists if you're using them. Tip #3: When importing and solving really tough puzzles, your browser may show 'Script running slowly' messages. Choose 'No' (IE) or 'Cancel' (Firefox) to let the solver keep on running. It'll get there in the end! Links: The Daily Sudoku. A new puzzle every day, plus lots of links. Daily Telegraph Sudoku. Puzzles and links, plus an excellent guide to solving techniques. Sudoku Solver. This Excelbased solver gave me the idea for the solver in this page  thanks! Mark Huckvale's Sudoku Workpad. Puzzle generator and solver. How the solver in this page works for anyone who's interested.
Switching symbols?
The big secret about sudoku is that it isn't really a number puzzle at all (it's
about logic). The characters 1 to 9 are a convenient set of symbols that we all
recognise, but they have no mathematical significance in this context.
Sudoku works just as well using shapes, colours  even vegetables ('each row
must contain a carrot, onion, potato...."). Any set of nine distinct entities
will do.
We can't stretch to vegetables here at paulspages, but we can manage a couple of
alternative symbol sets. The alphabetical ones are fairly easy, but the
punctuation symbols are harder, mainly because we don't have a preconceived
order for them (unlike 'ABC..'), so it's harder to work methodically through
them.
To switch symbol sets, just select a different set from the dropdown list. You
can do this at any time, without losing the current puzzle. (Note: manual
candidate lists won't be converted  sorry!)
Alternative symbol sets also work on the printer page, and import/export.
Go on  try it if you're tough enough!
