Tough Sudoku for 9/February/2007

Beautiful! I love the light effect from the stained glass windows opposite.

Nice stained glass

A proof for tough sudoku of 02 09 2007:

1) Start at 22 filled - the given puzzle. Unique Possibilities to 27 filled. (UP 27).
2a) Hidden pair 45 at h5i6 forbids h5=2, i6=7
2b) Locked 2's at ef5 forbids e4ef6=2
2c) Triplet 369 at f236 forbids f9=369,f8=39 UP 29
3) Hidden pair 78 at b2c3 forbids b2=13, c3=345 UP 42
4) Y wing style:b1=4 == a3=4 -- a3=5 == h3=5 -- h5=5 == h5=4 forbids b5,h1=4 UP 81

Sets:2+1+3+2+3 = 11
max depth 3 twice
Rating: .21

Y wing styles show up with such frequency, perhaps I will blog a page that details how to find them.
Often, I visit forums about sudoku and see some very complex and tortured explanation of how to advance a puzzle past a particular point - yet a simple Y wing style unlocks the entire puzzle.

If I post the easy Y wing style solution at such a forum, - it is often ignored as it does not fit into the predetermined patterns that they have established. As noted in the blog - such preconceptions are counter productive.

After fc's on just one candidate, Y wing styles are the next thing that I look for. Often, a puzzle has more than one of them available. Furthermore, they are much more common than a typical Y wing.

7:46 Maen 1 error

Good Maen all ! 16:09 which for me is getting better on Tough. Love the stained glass...it's a beautiful Cathedral.

Nice

This took way too long, but I love the prize of a beautiful picture at the end.

They sure don't make them like they used to. Just beautiful!

Not so easy. Made some mistakes and I pray.

is this the Washington National Cathedral i DC? I haven't been there in decades, but wanted to get married there.

It's always possible to do the toughies. Fill in all the possibilities & the uniques. Eliminate all easy forbidens and then switch to 'allow incorrect mode' Start filling in on a chain from a double or a triple and then follow it to the end. If it doesn't pan out try with the other number(s)from the original double or triple. It always works. Takes around 20min every time with never a mistake.

This looks like it would be a nice place to visit.

Have a great day everyone.

Hi Jax!
The method you describe is usually the most time efficient manner to tackle such a puzzle. However, many will find such a plan of attack feels too much like guessing. More precisely, it is known as Ariadne's Thread.

I have added another new blog page, Finding Ywing Styles.

A link to this page is in the upper right column, directly under 'Check out the Sudoku Blog'.

Hopefully, the procedure described for finding such eliminations will be helpful for many.

Hi everyone and nice maEn to all.
I like such stained glass fine art specially in churches and cathedrals as it gives a beautiful colour reflection which add more respection and quite to the place.

No guesses today!

32:45 I would like to see a simple explanation on how the Y wings work.

11:28; breathtaking glasswork! Don't like automatically removing possibilities as it reduces the mind-bending to simple data entry.

Steve, I got up to 28 or 29 filled by myself, then looked at your proof. I had missed the 369 in step 2c and added one more number but could not get up to 42, even tho I'd already found the 78 in step 3 (by the way, b3 and c2, not b2 and c3). Your Y wing style solved everything. Maybe your new blog will help me with these 'easier' toughs. Otherwise, I'll keep looking for your proofs or guessing. Thanks.

Beautiful cathedral. Have a terrific day/night, everyone!

15.34

I got stuck. I had to guess. I love stained glass.

Thanks Cami!
Sorry about the typo's!

7:53 could be better loved the pic!!

18:16 Hi to all. Beautiful windows

Love stained glass. I must be improving, 1:30 today , logic only
PS Thats 1hour30mins

10.34
beautiful windows

Not too bad. reductions, pointing pairs, more reductions, a 2-string kite, A hidden 58, eventually only conjugate pairs or triples (BUG+several). Too lazy to find the XYZ-wing(s) so started coloring. got lucky, my first chain was invalid making all the non-colored pairs correct, done. Fun. Regards all. Nice pic, tripod with a short timed exposure?

Beautiful stained glass

Liked this one.

SE=7.1

17:33.