dailysudoku.com

nataraj · Posted: Thu Oct 02, 2008 6:42 am Post subject: Oct 2 vh

I had a very good time solving this one (with a twist at the end)
After basics, there is a skyscraper (6) in rows 4 and 8, plus an x-wing (4) in rows 6 and 8.

After that,

Asellus · Posted: Thu Oct 02, 2008 9:03 am Post subject:

Not only does that 134 XY Wing have the same effect, it is all you need from the get-go to solve the puzzle.

nataraj · Posted: Thu Oct 02, 2008 10:30 am Post subject:

tlanglet · Posted: Thu Oct 02, 2008 12:33 pm Post subject:

Sorry to say that I saw the xy-wing <134> one-punch knockout. However I did the puzzle a second time and ignored it; three steps were required.

Ted

arkietech · Posted: Thu Oct 02, 2008 1:39 pm Post subject:

eddieg · Joined: 12 Jan 2006 Posts: 47 Location: San Diego, CA USA

Maybe some of both?

nataraj · Posted: Thu Oct 02, 2008 2:58 pm Post subject:

arkietech,
the pattern *-a-A-* in your grid is a w-wing.
Characteristics:
"the pincers": two identical bi-value cells (r5c2,r7c8 have two candidates 3 and 6) that do not share a house.

The "wing": both cells "see" the ends of a strong link in one of the two candidates (in this case the candidate is 3, the strong link is between r5c1 and r7c1)

The victim: Every cell that sees both pincers cannot contain the other candidate (6), so r5c8<>6.

The pincers act as a strong link (at least one of them must be 6), so we can construct another elimination altogether (not a w-wing), that gets rid of the 6 in r4c2. This other elimination is shown in my drawing. I gave the "shorthand" notation for this AIC
(6) r4c2-r5c2=[w-wing]=r7c8-r8c7=r4c7-r4c2
, what it means is:
if r5c2 is not 6 then (because of the w-wing) r7c8 is 6.
But then r8c7 is not 6, then r4c7 is 6.
r4c2 sees both r5c2 and r4c7 and therefore cannot be 6

Clement · Posted: Thu Oct 02, 2008 3:39 pm Post subject: Daily Sudoku: Thu 2-Oct-2008 VH

XY-Wing 134 Pivot {1,3}r7c1 with Pincers in r9c3{3,4} and r7c5{1,4} eliminating the 4's in r7c23 leaving 4 as the only candidate in r4c2. This solves the puzzle.

Marty R. · Posted: Thu Oct 02, 2008 3:53 pm Post subject:

nataraj · Posted: Thu Oct 02, 2008 5:20 pm Post subject:

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

The simple solution is the XY wing in boxes 6 & 7 BUT I used a solution albeit more complex but to me is interesting.

Looking for an XY I saw the 13 (box1) and 36(Box 4) and looking for a 16 to complete the XY I noticed the one in box3. No good BUT the 68s in col 9 connect the 36 to the 16 to give an XY 13 36 68 86 61 chain, eliminating 1 from r1c7 to give an easy solution.

I presume XY chains are "inferior" to XY Wings, But it didn't need the 68 link to be a naked pair (allowing a simple XY chain). Had the 6's been strongly linked in col 7 the same logic would have worked albeit no simple XY chain. Has this variant of an XY chain got a name?

Incidentally I often find recently , and so it was today, the the ranking (very Hard) does not appear on th print out. By using draw/play , and the tab "Today" followed by print, I get the grading!

Asellus · Posted: Thu Oct 02, 2008 11:33 pm Post subject:

keith · Posted: Fri Oct 03, 2008 12:28 am Post subject:

I am late to the discussion, and I have not read all the posts in detail. This one took not much time. After filling in the singles, and only candidates in those cells where there are two:

DennyOR · Joined: 12 Sep 2007 Posts: 33 Location: Portland, Oregon

My solution was the xy chain 34-46-69-91-13.

Since I look for xy chains instead of xy-wings, I'm as likely to find a long chain as a 3-member chain (wing). Flitting around from one linked pair to the next to see if I can find any matched ends that eliminate numbers is my sudoku fun time. I find the rest of process of solving a sudoku to be tedious (but still satisfying).