Sudoku Puzzles

Perfectly positioned photo Keyan!

On the third day of Christmas my true love sent to me ... three French hens!

Where is everyone thi morning?! Twenty past the hour and I seem to be first!

Good morning to all! Interesting picture Keyan! Well done.

7:03 Not hard today
Great Photo!

This looks like a picture out of the future.

Nice, nice & nice.

Great photo. Great underground system mostly built in the 1980's--way ahead of its time.

Another incredible picture, Keyan, thanks for sharing it. The trains/station sure didn't look like that when I left there.

57:20 - not easy today.....

great pic, i think my brain is running on empty after the holiday weekend. I cant wait to get away from work for a full week in january! yay for having PTO! 31:28 today, awful time.

The blog has a new page: Coloring.
You can find the link at the top right corner of the page.
Coloring is one of my favorite techniques.... - guess it is the child in me.
Visit for an in depth explanation

A proof for tough sudoku of 12 27 06:
1) Start at 23 filled - the given puzzle. Unique Possibilities to 26 filled. (UP 26).
2) c7=5 == e7=5 -- e7=2 == e46=2 -- df5=2 == b5=2 -- b5=3 == c5=3 forbids c7=3 UP 81
Sets: 4. Max depth 4. Rating .15 Non-native eliminations required 1:

Today's puzzle is an excellent example of using swordfish to find fc's:
The swordfish on 5's and the one on 2's available in today's puzzle clue one into if
a relationship between 2's and 5's is found that the puzzle may unravel.

The blog will eventually not only explain forbidding chains, but also present general tips on where to look for them.

maEn all!

Thanks! I was hugely impressed with the DC metro. It was the Thanksgiving holiday, and so not crowded. The strength and grace of the lines were amazing. It was like entering a great sculpture or monument.

Needed a couple of guesses today.

Very cool pic. Not far from home; maybe I'll check it out sometime. Wish I understood the solution jargon.

Wow, the first picture I knew immediately, not from TV, books, or travels abroad. Now I'm trying to guess which station it is, since they don't all look the same. Mine has a center platform like this one, but it isn't my station.

Hi Steve,
1. Once you told us that c7 can't be 3 I could see why. but how do you find it?
2. The terms : sets, depth, rating, non-native elimination come from some program. Which?
Happy new year!
Gaby

Hi Gaby!
In a puzzle like today's:
After making all the easy type eliminations:
pairs, triples, locked sets, swordfish,etc.
I print out the puzzle.
I circle the endpoints of strong links that have only two choices.
I underline one endpoint of a strong link that crosses boxes.
I More...

Question one: cells that have one circle and one underline are also focus. In today's puzzle, cells:
c7,e7,b5 have two circles, each. This gives some clue that focus could go there.
Then - recognizing the coloring like transference on 2's (of which there are more after doing the swordfish, but enough without it)
produces the fc.

A tough one.

Nov. 5, 2007.

SE=7.2