## Guess with pencil marks? (Sunday Times #16 (2005.Nov.13))

Post the puzzle or solving technique that's causing you trouble and someone will help

### Guess with pencil marks? (Sunday Times #16 (2005.Nov.13))

Today's Superior Sudoku in the Times (13/11/05) I could not solve, even with pencil marks, by logic alone.

I got to the point where I could not find a logical next step and I phoned a friend who had exactly the same numbers in and exactly the same pencil marks as me but she too was stuck.

In the end we resorted to trying one of the numbers in a cell with only two numbers in then working through until we got stuck. Then trying the other number worked through to a completed solution.

Is today's Superior solvable by logic alone? Are we both missing something?
confucious

Posts: 3
Joined: 13 November 2005

Today's Superior Sudoku can be solved with logic alone, a property of all pappocom puzzles.

It takes a lot of tricks to solve this puzzle, if you are not used to solving difficult puzzles take a look at

http://www.angusj.com/sudoku/hints.php

pay particular attention to the Swordfish section, this is the first trick you need to use.

also worth a look are hidden pairs and x-wings.

post your puzzle where you are stuck if you need more help.

edit: there is a swordfish in this puzzle, but it can be solved with just using a x-wing

... try looking at the lucky number 7 ! !
Last edited by Crazy Girl on Sun Nov 13, 2005 7:55 pm, edited 1 time in total.
Crazy Girl

Posts: 189
Joined: 08 November 2005

It should be doable. The most likely thing you're missing (though I haven't looked at this particular puzzle) is what's called an "X-Wing". It's a tad complicated, but if you do a Google search for "Sudoku X-Wing" or something I'm sure there are websites that can explain them (maybe someone else has the URLs?).

Edit: darn, beaten to it. Although you should never need a Swordfish for a Pappocom puzzle. The only tactic you need in Sunday ones that you never need in weekday puzzles is the X-Wing.
PaulIQ164

Posts: 533
Joined: 16 July 2005

### can be solved with X-Wing

I solved it using 2 X-Wings

It is a really interesting one.
aleph

Posts: 9
Joined: 03 August 2005

I solved it using 2 X-Wings

It is a really interesting one.

Yes, 2 x-wings did it for me. As Crazy Girl says, one of them involved 7s but I needed another one before then.
Bigtone53

Posts: 413
Joined: 19 September 2005

I solved this one quite quickly and wasn't aware of using X wings (although that doesn't mean I didn't......).
dalek

Posts: 17
Joined: 28 September 2005

As previously remarked this one certainly was interesting.

It was a real pleasure to be able to use a swordfish on this one, as I rarely have the experience. From the other comments, I know that using a swordfish was not necessary, but that doesn't lessen the fun of applying it to this puzzle, and may have contributed to helping me to solve it quicker.

IMO these patterns were easier to see in this puzzle than usual, because there were relatively few empty squares, with only a few candidates.

I hope that the next one is as interesting
Heuresement

Posts: 54
Joined: 19 August 2005

Many thanks for all your help and advise - I have a lot to learn.

This weeks didn't even need pencil marks!
confucious

Posts: 3
Joined: 13 November 2005

### re: The Sunday Times #16 (2005.Nov.13)

aleph wrote:I solved it using 2 X-Wings

It is a really interesting one.
Bigtone53 wrote: Yes, 2 x-wings did it for me. As Crazy Girl says, one of them involved 7s but I needed another one before then.

there are indeed 2 X-wings available, but Crazy Girl is right -
only one is needed, the other one is a red herring.

- Pat

Pat

Posts: 3653
Joined: 18 July 2005