dailysudoku.com

Johan · Joined: 25 Jun 2007 Posts: 206 Location: Bornem Belgium

A double wing-move collapses the grid.

Marty R. · Posted: Sun Sep 16, 2007 12:32 am Post subject:

How do you already have the puzzle for the 16th when I click and still see the 15th? Question

Is Sam updating by time zones?

kragzy · Joined: 01 May 2007 Posts: 112 Location: Australia

It appears that the puzzles load up according to your local time. I have been aware ever since I started doing my Daily Sudoku last year that we Aussies get to see the puzzle well before others. I always have to wait until the next day to have a look at any discussion that may have been generated.

If you want to get the earliest possible glimpse, then perhaps you should find a New Zealander or Fijian to copy and email it to you. Very Happy

kragzy · Joined: 01 May 2007 Posts: 112 Location: Australia

By the way, I didn't need any higher tricks, not even locked candidates, for this VH. It was a Medium at best. Perhaps I was just lucky.

Johan · Joined: 25 Jun 2007 Posts: 206 Location: Bornem Belgium

George Woods · Joined: 28 Mar 2006 Posts: 304 Location: Dorset UK

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada

sdq_pete · Joined: 30 Apr 2007 Posts: 119 Location: Rotterdam, NL

I'm afraid my old brain got stuck on this one. Here's the position I reached:

TKiel · Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

I ignored both XY-wings in Boxes 3&6, and used mostly W-wing's or W-wing's with coloring to reach this BUG+1.

TKiel · Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

Peter,

Look at Box 4.

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada

Strange. After looking at Pete's grid I saw that I had missed a very basic step. I was consequently able to finish without a single "clever" step. Is Kragzy correct - is this not a VH or did me and him screw up.

TKiel · Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

There were at least a couple of points where an XY-wing was the simplest move (depending of course on how one ranks the various techniques).

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada

Pete - how did you get the 7 in R3C5.

kragzy · Joined: 01 May 2007 Posts: 112 Location: Australia

I just re-did this puzzle to see if yesterday's attempt was a fluke. It was. I needed two XY wings this time. I must have made an error in my lazy Sunday afternoon approach that turned to be lucky.

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada

I also redid it - and used 2 xwings, one xyz wing and a skyscraper. Not an easy one eh.

Marty R. · Posted: Mon Sep 17, 2007 3:41 pm Post subject:

I had a heck of a time with this; obviously missed something based on other posts. Two XYZ-Wings, three rectangles, a W-Wing and an XY-Wing with coloring finished it off.

sdq_pete · Joined: 30 Apr 2007 Posts: 119 Location: Rotterdam, NL

George Woods · Joined: 28 Mar 2006 Posts: 304 Location: Dorset UK

Having looked at sdq_pete's grid I realised I had erroneously claimed an XYZ wing based on r3c8 being 12 - eliminating the 2 at r4c8 - but of course I had misread 12 - and it really is 13 so the xyz wing removes the 3 from r4c8 as recognised by sdq_pete, but doesn't seem to lead anywhere. Further I couldn't see any obvious answer to sdq_pete's grid, via the discussion. The position is pretty much where I got to (after an XY wing and an XYZ wing plus the "useless" XYZ wing mentined above)

So for me the puzzle had to be solved again properly, 'cos my lucky mistaken elimination of the 2 from r4c8 is not valid on this argument. -- But hang on!!
If r4c8 is 2 then r5c7 is 3 and r4c9 is 7 making r1c9 3 and no room for a 3 in col 8! So yes the 2 at r4c8 can be removed giving a straightforward solution.

So this solution will be classed as a forcing chain- but it so short and the argument doesn't need pencil and paper - so I claim it is logical -albeit not one beloved of those that use rules that might be built into a computer program!!!!!

Can someone transform this solution into a more "acceptable" form?

Asellus · Posted: Mon Sep 17, 2007 10:58 pm Post subject:

George,

I don't know how "acceptable" this is, but perhaps the easiest way to see it consistent with common techniques is as the overlap of an X-Wing with a W-Wing-like structure.

First, the X-Wing is on <7> in R14C89.

The "not quite W-Wing" involves the bivalue cells at R5C7 and R1C9, {23} and {37} respectively. Note that there is an external strong link on <3> in Box 9 between C7 and C9. This means that one or both of the bivalues cannot be <3>. Thus, R5C7 is <2> and/or R1C9 is <7>.

If R5C7 is <2>, R4C8 cannot be. If R1C9 is <7>, then so must be R4C8, due to the X-Wing. So, again, it cannot be <2>. So, <2> is eliminated.

(It is of course possible to construct a chain notation; but, I believe it would be a bit messy.)

Maybe someone can see some other angle on it. I tried without success to see it as an ALS or Sue de Coq type of elimination.

Jeff · Joined: 06 May 2007 Posts: 46

I have read all the posts on this puzzle and I simply can't figure out what to do next. Here is my current progress.