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Tough Sudoku for 27/May/2006


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Submitted by: Gath

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we have a symetrical one today, thanks Gath :))
Strange looking cat!
well, that's my guess :)
And we get excited over seeing a praying mantis...
12:52..is that a 19' monitor?? haha...I slay me

Poor little guy just wanted a hot bath...
Ahh! One of our water dragons! We back onto a little bit of bush right where it comes out a stormwater canal but still lots of native animals including these lizards! We had baby water dragons last spring ... so cute! Good Night all!
Jim, are you sure you are in Manaus?
This is a dragon, not a cat. Take care!!
Water dragon:
http://www.anhs.com.au/eastern_ water_dragon.htm
I think monitor lizards are smoother - less spiky!
From Mallorca to this?
A reasonably easy tough today. The following is a possible approach:

1) Start at 22 filled - the given puzzle. Unique Possibilities to 24. (UP 24)
2) Hidden pair 14 at b9,h9 forbids 6 from b9 and forbids 35 from h9. UP 30
3) Locked 5's at def9 forbid 5 from de8 and df7.
4) More...
14:28. I don't like the way he's looking at me...
I did this independently of Steve and came up with a very similar proof.

1) Start 22, UP to 24.
2) Since b5=2 == c4=2 -- e4=2 == e58=2, and also b5=2 == b8=2 -- e8=2 == e45=2, we have b5=2 == e5=2. This forbids d5=2 and f5=2.
3) Naked triplet d9=356, e9=35, f9=356 forbids b9=6, h9=35, More...
I'm ecstatic - I got out a tough! Must have been very easy! Nice present for the weekend, though.
Glad I missed seeing those when I was there.
I would guess that the place I stayed in Castle Crag might have had them if not for the resident free roaming cat. The anole in Florida are much cuter.
10:44, did pretty well all the way through it.
Good mAen to all. A 'hot' water dragon?? Must have some fire in it!
Improvement on my proof - should have seen this earlier, but realized while driving about....
1) Start at 22 filled - the given puzzle. Unique Possibilities to 24. (UP 24)
2) Hidden pair 14 at b9,h9 forbids 6 from b9 and forbids 35 from h9. UP 30
3) Locked 5's at def9 forbid 5 from de8 More...
nice dragon. Amazing i got through all of these sudoku puzzles in 5 minutes flat.
Nice proof Clark! In your step 2, you only need the later chain to forbid the 2's at df5. It is always interesting when proofs for a puzzle are so similar, albeit for this particular puzzle, I think that the paths to take to solve it are fairly clear.

You're right about that chain. I would have seen it if I had read it in someone else's proof. :) It was actually a coloring step I converted into chains, so I didn't look at the chains when I wrote them out.
Nice dragon Kate You are so lucky for them to live there not many in suburbs any more ............We had to send one to dream land a few weeks ago victim of a lawn mower lost the top of its head and after many months it did not recover and was later proved to be brain dead poor thing.
Physignathus lesueurii.........Sole aust member of genus one other is found in south east asia. These Dragons have addapted well to water ways in Sydney Canberra Brisband and Melbourne Could not tell from photo if Male or female
We have many of those in our area too! Fascinating.
To b from Washington

Thanks for the hints Steve and Clark. Those short chains to eliminate 2s really sorted that puzzle.

I like that Eastern Water Dragon. Great that they are still hanging around Sydney and such places.

When I was living out bush I had 3 frilled neck lizards that regularly climbed More...
Would someone pls translate Steve's & Clark's comments about forcing chains into plain English? e.g.'d3=1 == g3=3 -- g7=1 == h7=1 -- h7=9 == f7=9 -- f7=2 == f3=2 forbids d3=2'. I understand the cell references, but how do I read '==' & '--'?
Hi Richard!
The link 'proofs' below provides further links which explain 'forbidding chains'.

In general: (let A, B be boolean variables)

A == B means: A OR B.

A -- B means: (notA) OR (notB).

How these chains then reach the conclusions above can also be found in the links described above.
Steve, thanks very much. I understand now!
Well done to all those who have 'formulae, chains and great systems'. This was a hard one for me and once I had placed all possibilities in and STILL couldn’t work it out, I’ll admit to turning off “Allow incorrect Moves” and had great flashing red-guesses. My motivation was to see the photo- which are usually great.
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July 27, 2007.
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