Tough Sudoku

1) Start at 23 filled - the given puzzle. Unique Possibilities to 28. (UP 28) (solve all the sixes).
2) Locked 2's at d46 forbid d12=2. UP 32.
3) Hidden pair 38 at d2, f3 forbids d2= 459, f3=49.
4) Locked 4's at d23 forbids d89=4. UP 36.
5) i7=8 == i3=8 -- g2=8 == d2=8 forbids d7=8.. UP 81.

Total sets: 1 + 2 + 1 + 2 = 6. Max depth 2.
Proof difficulty rating: .01 + .03 + .01 + .03 = .08. Less than .1 is trivial, I think

9:29 Maen

Yesterday, some asked for explanation of terminology. Check proofs link below.

Step 5 above is standard 'coloring' presented as a forbidding chain:
If i7=8, then d7<>8. If i7<>8, then i3=8, then g2<>8, then d2=8, and d7<>8. Thus, in any event, d7<>8.

Easy today

Must have been easy today. I didn't need any guesses!

What a handsome family.

16:08
Is this a good time?
I tried it without any random guessing.
Usually I am in the 20+ range.

Timer 00:07:25

Hurried through proof above: It can be improved upon, though it is hardly worth it:

1) Start at 23 filled. UP 28
2) Locked 2's at d46 forbid d12=2. UP 32.
3) Pair 59 at d1,f1 forbids d2=5, d2,e23,f3=9. UP 36.
4) i7=8 == i3=8 -- g2=8 == d2=8 forbids d7=8.. UP 81.

Total sets: 1 + 2 + 2 = 5. Max depth 2.
Proof difficulty rating: .01 + .03 + .03 = .07.

24:00

20:07 super slow,brain fog
Deb...my daughter wants to know if your son is coming over to Kansas anytime soon...if so, she says, look us up. What a cutie!

10:04, my best time yet! I only made about five mistakes but once they where fixed I easily finished. That was fun!

TOUGH SUDOKU CHAIN FOR DUMMIES (like me)
placed all my possibilities==hmmm=== guessed==flashes of red==oh no== stable green== automatic removal. Then another guess== green, guess again==flashing red== oh bother, try again. Okay done.
cute family Deb.

Slightly different to Steve but amounts to the same thing - UP 36 then if i3=8, d2&7=8, which can't be, therefore i7 must =8., UP 81.

14:12 and only 1 red flash. Wow

Very Easy Tough today. No guesses for me! Yea!

Mandy from Perth -- Very funny!

MB from DE USA (where is that by the way?)
I wasn't trying to be funny....that is how I REALLY solve most of the tough ones

mAen,
This was easier than the hard for me today for whatever reason.

Good looking kin, my daughter made the same comment as Cinji's did!

Mandy's ingenious technique:
Guess: red flash == green flash: forbids wrong guess . prn. easy to end.

Andrei: applying the general idea of matrix construction to a set of possibilities, it seems that one can construct a rather full matrix in some situations that will imply a group of non-native strong sets. Of course this is obvious with constructs like swordfish, etc. The very tough tough of 4/2/06 -- it seems to me that there is some significant benefit to writing a proof of that ugly monster using matrices and abandoning forbidding chains. 'Tis something I may have to add more often.

It also seems that complicated forbiddings using groups of almost locked sets - and almost almost locked sets - will become not only more transparent, but less complicated with some matriz techniques. Perhaps more investigation into this area is warranted.

Although one can write most (if not all) such techniques as forbidding chains (using partitions of sets, rather then the standard nomenclature) - using matrices seems to make that exercise somewhat laborious.

Deb - by any chance is your son thinking of going to the University of Florida? My daughter starts there in a couple months and...

Good mAen to all. Thanks for letting us get to know your family Gath!!

7:06

8:21 good mAen all! good looking family!

18:04 Deb, your whole family is a photographer's dream. You should be very proud!

Nice looking young man & adorable little lady!

38'00, with reference to Steve's first proof. On my own I began looking at the same 8's that he did, but failed to take d7 into consideration. Bother.

I still don't understand colors. Is there anywhere to go look up an explanation? Anymore I can't get here every day, and if I miss even a few days in a row there get to be mountains of information to sort through. I also can't usually get here early in the day, either. I'd be grateful to anyone who can post my query early so that more people may have a chance to respond...

I have heard of lock up your daughters but after seeing the pic and reading the comments I think in this case it is lock up your son Very nice young Gentleman deb The sun is out but still very cold and loving it

I have stumbled on something new and wonderous!!!(OK, well some of you have been suggesting this for months now, but it takes some of us in the rut longer to climb out) I didn't time myself and I really enjoyed it!

It is certainly a case of 'lock up your sons', Glynnis - I even went 'Mmmm. Yummy.' and I'm over 40. I'm a sad sick woman.

MANDY from Perth -- glad you asked! Delaware is the second smallest state in the US. (Rhode Island is the smallest.) We are just south of Philadelphia and halfway between Washington, DC, and New York City on the train (Amtrak).

As to why I said it was funny -- it was so real for me, and such a good parody of the proofs of those who are way more into mathematics/logic than I!

GLENN -- Ah, Gainsville! What a nice college town. (I visited there several years ago.)

14:15 went well till I got stuck. Untangled the chain using Steve's Step 5 and I was away again. Thanks Steve.
Which Deb owns up to these beautiful people. My 17 y.o. daughter would say he was 'hot'. Deb from Bris., is he yours? How old is he?

Larryville/ks usa - Untick 'Allow incorrect moves' in the boxes under the puzzle, then if you put the wrong number in a cell it will flash red to tell you that it's wrong. If it is correct, then it shows green. I do this when I am really stuck on a puzzle and I start guessing, then I know if my guess is right or wrong before I go too far.

Nice looking little boy. He seems to be fuul of life and looking to find something or someone---perhaps, mom?

21:42 But I think one of my 'logical' deductions may have been a guess. (I think my chain went awry somewhere as I couldn't replicate it later.) Oh well, at least I can do some real work now!

Larryville,
Try this site:http://www.angusj.com/sudoku/hints. php

19:12

Larryville,
Sorry, there is a space between the . and the php. Try http://www.angusj.com/sudoku/hints.php

fine looking boys

10:34 with a lucky 'guess'.
wow, Deb must be beautiful too! a niece with lots of blonde curls, and a spunk of a son, who obviously doesn't mind entertaining the littlies. what a great family! oh wait, is this the Deb from Brisbane who we saw a while back with her daughter? definitely beautiful genes in the family.

alana is a girl's name, and that looks like a little girl to me. Or am I wrong? there seems to be a bit of confusion on the site about the younger one's gender!