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

Very hard has now included X wings aa a technique that must be used to solve. But today's seems to use a Unique Rectangle- unless you know better.

The solution proceeds without even using a hidden pair, until a crunch point where 49 s in col1 r 7 and 9 and r9c6 denies either 4 or 9 in r7c6 and so on to the solution.

So is this use of unique rectangle a first, and is it the only way?

keith · Posted: Sun Jun 04, 2006 12:07 pm Post subject: One way

You can solve it with an X-wing.

Keith

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

Multiple colouring/strong links on 6's also solves it.

kkklau · Joined: 31 May 2006 Posts: 2

x wing of 6 at column 3 and 5
after that it's straight forward

gigi · Joined: 04 Jun 2006 Posts: 5 Location: Central Texas

Howdy from Texas y'all... I'm so hooked on Sudoku! I've been visiting here from time to time to solve the puzzles and learn new techniques.

But in regard to today's puzzle (June 4 - VHard), I found that the X-Wing solution that kkk posted (solve off the 6 in Cols 3 and 5) didn't work for me. I thought I was losing my mind! Shocked

Not sure where I went wrong.... (E-mail me kkk if you can figure out how I messed up)

But...

I did X-Wing off the 9's in Cols 1 and 6 and solved it with no problem.

I did a little more reading on X-Wing techniques just to confirm I wasn't going nuts... (still consider myself a novice for the most part)... and here is a good explanation how X-Wing works for anyone that is interested.... Unlike the 6's in kkk's post, I played off the 9's because there were no other options for the 9's in those rows as discussed in the following link!!

http://www.sadmansoftware.com/sudoku/technique6.htm

Have a great week!

gigi

[url][/url]

Marty R. · Posted: Sun Jun 04, 2006 9:12 pm Post subject:

After filling in the cells with their candidates and using basic techniques to eliminate candidates, I noticed in rows 36 and columns 89, a “Type 1” rectangle of 57-57-57-3567. Thus, the 57 gets eliminated from the fourth cell, leaving a 36. After more basic eliminations, I see another Type 1 rectangle in rows 79 and columns 16 of 49-49-49-1469. So the 49 is removed from the last cell, and that allows the puzzle to be completed with basic techniques.

In this thread, we have seen mention of X-Wings, Unique Rectangles, Multiple Coloring and Strong Links. It seems that I am writing every other day how it never ceases to fascinate me how many different approaches and techniques can be used to solve a given puzzle, and this one is certainly no exception.

keith · Posted: Sun Jun 04, 2006 10:17 pm Post subject: Here is the grid

Here is the grid:

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

Keith
I was revisiting and looked at your "crunch point" with 1 x wing and 2 URs.Another UR you didn't mention is the 16 in r39 c35 The need for a 3 in this makes r2c5 1 and it solves so quickly after this one that it must be an A grade move!!!!

David Bryant · Joined: 29 Jul 2005 Posts: 559 Location: Denver, Colorado