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xyz wing sudoku strategy

XYZ-Wing - SudokuWiki.org
www.sudokuwiki.org
Sudoku Strategy. XYZ-Wings extend Y-Wings to three numbers and are three cell formations used to eliminate candidate elsewhere.
Wings (XY-Wing, XYZ-Wing, W-Wing) - HoDoKu
hodoku.sourceforge.net
Solving Techniques for sudoku - Wings (XY-Wing, XYZ-Wing, W-Wing) ... The possible candidates in that cell are called X and Y. Now we try to find two other ...
Solving Technique - XYZ Wings - Sudoku Snake
www.sudokusnake.com
An XYZ-Wing is like an XY-Wing in that it is a group of three cells, one sharing a unit with the other two. However, the first cell in an XYZ-Wing has three ...
XYZ-Wing Strategy - Sudoku Solving Techniques
www.sudoku.org.uk
It gets its name from the three numbers X, Y and Z that are required in the hinge. The outer cells in the formation will be XZ and YZ, Z being the common ...
Sudoku X-Wing Identification And Solution
www.sudokuessentials.com
Sudoku X-Wing can solve some of your most difficult Sudoku puzzles. This illustrative article will help you become a puzzle pro.
XYZ-Wing - Sudoku Solving Techniques
sudoku9x9.com
XYZ-Wing ... The yellow cell XZ shares a common 3x3 box with the red cell XYZ and the green cell YZ shares a common row with the red cell XYZ. These three cells ...
Sudoku X-Wing technique: when and how to use
www.sudokuonline.io
Requirements to apply the Sudoku X-Wing strategy ... To be able to apply this technique, the player must find 2 rows or 2 columns where a single digit is a ...
X-Wings – Sudoku of the Day
www.sudokuoftheday.com
Solving Sudoku : X-Wings ... X-Wings are fairly easy to spot, but a little harder to understand than some other techniques. Like others it relies on using ...
X Wing - Learn Sudoku
www.learn-sudoku.com
An X Wing is a technique for removing candidates (pencil marks). It starts with either two parallel rows or two parallel columns.
X-Wing Strategy - Sudoku - Thonky.com
www.thonky.com
X-Wing is a strategy in which you find a candidate that appears twice in two different rows, and those appearances are both in the same ...
X Wing - Sudoku Beginner
www.sudokubeginner.com
X Wing is an advanced sudoku technique, which means that the end result will not necessarily be finding the number that goes in a cell.
Solving Techniques 10- XYZ-Wing
nanpre.adg5.com
The XYZ-Wing is different from XY, in that three numbers are used. It is like the diagram below. When a problem turns out like this, a 3 will be entered ...
Sudoku XYZ-Wing Strategy explained
www.taupierbw.be
XYZ-Wing ... Indeed, the "Three-Value" Cell and the two "Bi-Value" Cells form a group of three Cells with exactly three possible candidates, so their solution ...
Watch XYZ-Wing Solving Techniques - Sudoku Swami
sudokuswami.com
In an XYZ wing there are three cells and three candidates. It will have a configuration where one of the pincers will be in the same block as the pivot cell ...
XY Wing aka Y Wing Sudoku Ultimate Technique
www.livesudoku.com
XY Wing (sometimes called Y Wing) is another advanced technique for eliminating candidates. It starts by finding a cell with only two candidates (a bi-value ...
Printable Puzzles by KrazyDad
krazydad.com
The following list of Sudoku Solving Techniques is based on a collection of tips ... Swordfish is on the same principle as X-wings, but extended to three ...
WXYZ-Wing - Solving sudoku strategy
www.sudoku9981.com
Introduce sudoku solving technique : The WXYZ-Wing is an extension of the XYZ-Wing, and is sometimes called XYZW-Wing. Seeing the extension of XYZ-Wing to ...
Sudoku Solutions, Advanced- X-wing, XY-Wing, Swordfish
www.puzzles-on-line-niche.com
These Sudoku solutions techniques are for the serious Sudoku addict! These are very involved tactics and require extensive knowledge of Sudoku puzzle ...
Sudoku Assistant -- Solving Techniques - St. Olaf College
www.stolaf.edu
In fact, though, X-wings and swordfish are simply two simple varieties of a much broader category of beast. A 5x5 circuit containing the candidate number "1" ...
Expert Sudoku Strategy XYZ-Wing Explained - YouTube
www.pinterest.com
X-Chain , How to solve sudoku puzzles - Solving sudoku strategy. Introduce sudoku solving technique : X-Chain .The X-Chain technique and the Multi-Colors ...
Xy wing sudoku manual | Peatix
xy-wing-sudoku-manual.peatix.com
a strategy all sudoku experts must know. these three cells form a xyz- wing pattern. this square is sometimes called a pivot or hinge. solving sudoku - xy- ...
100 Hard X-Wing Sudoku: Media, Clarity - Amazon.com
www.amazon.com
Practice your advanced sudoku-solving skills with these 100 hard sudoku puzzles , all of which will require you to use the X-wing solving technique in order ...
XY-Wing: Advanced Solving Sudoku Technique
www.createclassicsudoku.com
XY-Wing is a method used to refine the candiates of a square with multiple candiates. ... When one square with candidates {X, Y} is in the same row, column, ...
Irregular (W)XYZ-Wings : Advanced solving techniques
forum.enjoysudoku.com
As per my understanding, Irregular XYZ-Wings strategy is summarized as ... wings from what I understand from reading daily sudoku forums.
XY Wing - Sudoku Helper
sudoku.ironmonger.com
The XY Wing strategy uses three cells that contain two and only two candidates and have ... the XY Wing strategy is not related to the X Wing strategy.
Sudoku Solving Guide - SudoCue
www.sudocue.net
When you check the pattern for a digit, you may spot a set of locked candidates, alongside an X-Wing. Chances are slim that you stumble ...
Sudoku Puzzles by using x-wing techniques
oaji.net
The purpose of this essay is to implement and study different techniques for solving Sudoku puzzles, a problem similar to graph coloring with.
Basic & advanced Sudoku elimination techniques to solve ...
humage.com
Learn about solving Sudoku puzzles with various important techniques, such as X-Wing and Swordfish, all illustrated with clear pictures and detailed ...
Sudoku Fortschrittliche Lösungstechniken
www.janko.at
X-Wing, Swordfish, Jellyfish, Squirm Bag, Turbofish, Finned X-Wing, Sashimi Finned X-Wing ... This strategy works in the other direction as well.
omerfarukeker/Sudoku-Solver - GitHub
github.com
Solves the user entered Sudoku boards with commonly known strategies like hidden/naked pairs, X-wing, Y-wing etc. - GitHub - omerfarukeker/Sudoku-Solver: ...
Stuck at Sudoku? Here Are A Few Strategies To Get You ...
www.shawanoleader.com
This technique works with cells forming a rectangle, and it also occurs in rare situations. X-Wing is a pattern spanning multiple columns and ...
How to solve a Sudoku? - Telenet
users.telenet.be
A XY-Wing or XYZ-Wing with all cells in a same unit, is a naked triple with the values {X,Y,Z}. The next example shows how different solving techniques can be ...
How To Solve Sudoku Puzzles
puzzlebooksplus.com
Logic Techniques for Solving Sudoku ... You can use the X-Wing technique when a candidate number appears at all four corners of a rectangle, AND it is not a ...
XYZ - Wings - Speed Sudoku • View topic
www.speedsudoku.com
This is an extension of Y-Wing or (XY-Wing). John MacLeod defines one as "three cells that contain only 3 different numbers between them, ...
sudoku snake techniques
nkrafa.rtaf.mi.th
Sudoku X is played exactly the same way as the classic Sudoku, by filling in the numbers 1 through 9 in ... Sudoku Snake - Solving Technique - WXYZ Wings.
Finned X-Wing - Sudoku Solver
sudokusolver.app
In the sudoku diagram below, either in the R4C3 or R5C3 cells (marked in yellow) you can place the digit 6 or you have the X-Wing pattern, i.e. in the third ...
Please Give WXYZ Some Space | Systematic Sudoku
sysudoku.com
My early post on the regular XYZ-wing just passed “W” off as the rare ... with that in his Strategies page, presenting them as WXYZ-wings ...
Видео xyz-wing - imperiya.by
imperiya.by
Онлайн — Видео xyz-wing — imperiya.by. ... Advanced Solving Sudoku Technique - X-Wing ... Advanced Sudoku Strategy X-Wing Explained. ▻. RFC963 5 год.
XYZ-Wing - SudokuWiki.org
www.sudokuwiki.org
Sudoku Strategy. XYZ-Wings extend Y-Wings to three numbers and are three cell formations used to eliminate candidate elsewhere.
Wings (XY-Wing, XYZ-Wing, W-Wing) - HoDoKu
hodoku.sourceforge.net
Solving Techniques for sudoku - Wings (XY-Wing, XYZ-Wing, W-Wing) ... The possible candidates in that cell are called X and Y. Now we try to find two other ...
Solving Technique - XYZ Wings - Sudoku Snake
www.sudokusnake.com
An XYZ-Wing is like an XY-Wing in that it is a group of three cells, one sharing a unit with the other two. However, the first cell in an XYZ-Wing has three ...
XYZ-Wing Strategy - Sudoku Solving Techniques
www.sudoku.org.uk
It gets its name from the three numbers X, Y and Z that are required in the hinge. The outer cells in the formation will be XZ and YZ, Z being the common ...
Sudoku X-Wing Identification And Solution
www.sudokuessentials.com
Sudoku X-Wing can solve some of your most difficult Sudoku puzzles. This illustrative article will help you become a puzzle pro.
XYZ-Wing - Sudoku Solving Techniques
sudoku9x9.com
XYZ-Wing ... The yellow cell XZ shares a common 3x3 box with the red cell XYZ and the green cell YZ shares a common row with the red cell XYZ. These three cells ...
Sudoku X-Wing technique: when and how to use
www.sudokuonline.io
Requirements to apply the Sudoku X-Wing strategy ... To be able to apply this technique, the player must find 2 rows or 2 columns where a single digit is a ...
X-Wings – Sudoku of the Day
www.sudokuoftheday.com
Solving Sudoku : X-Wings ... X-Wings are fairly easy to spot, but a little harder to understand than some other techniques. Like others it relies on using ...
X Wing - Learn Sudoku
www.learn-sudoku.com
An X Wing is a technique for removing candidates (pencil marks). It starts with either two parallel rows or two parallel columns.
X-Wing Strategy - Sudoku - Thonky.com
www.thonky.com
X-Wing is a strategy in which you find a candidate that appears twice in two different rows, and those appearances are both in the same ...
X Wing - Sudoku Beginner
www.sudokubeginner.com
X Wing is an advanced sudoku technique, which means that the end result will not necessarily be finding the number that goes in a cell.
Solving Techniques 10- XYZ-Wing
nanpre.adg5.com
The XYZ-Wing is different from XY, in that three numbers are used. It is like the diagram below. When a problem turns out like this, a 3 will be entered ...
Sudoku XYZ-Wing Strategy explained
www.taupierbw.be
XYZ-Wing ... Indeed, the "Three-Value" Cell and the two "Bi-Value" Cells form a group of three Cells with exactly three possible candidates, so their solution ...
Watch XYZ-Wing Solving Techniques - Sudoku Swami
sudokuswami.com
In an XYZ wing there are three cells and three candidates. It will have a configuration where one of the pincers will be in the same block as the pivot cell ...
XY Wing aka Y Wing Sudoku Ultimate Technique
www.livesudoku.com
XY Wing (sometimes called Y Wing) is another advanced technique for eliminating candidates. It starts by finding a cell with only two candidates (a bi-value ...
Printable Puzzles by KrazyDad
krazydad.com
The following list of Sudoku Solving Techniques is based on a collection of tips ... Swordfish is on the same principle as X-wings, but extended to three ...
WXYZ-Wing - Solving sudoku strategy
www.sudoku9981.com
Introduce sudoku solving technique : The WXYZ-Wing is an extension of the XYZ-Wing, and is sometimes called XYZW-Wing. Seeing the extension of XYZ-Wing to ...
Sudoku Solutions, Advanced- X-wing, XY-Wing, Swordfish
www.puzzles-on-line-niche.com
These Sudoku solutions techniques are for the serious Sudoku addict! These are very involved tactics and require extensive knowledge of Sudoku puzzle ...
Sudoku Assistant -- Solving Techniques - St. Olaf College
www.stolaf.edu
In fact, though, X-wings and swordfish are simply two simple varieties of a much broader category of beast. A 5x5 circuit containing the candidate number "1" ...
Expert Sudoku Strategy XYZ-Wing Explained - YouTube
www.pinterest.com
X-Chain , How to solve sudoku puzzles - Solving sudoku strategy. Introduce sudoku solving technique : X-Chain .The X-Chain technique and the Multi-Colors ...
Xy wing sudoku manual | Peatix
xy-wing-sudoku-manual.peatix.com
a strategy all sudoku experts must know. these three cells form a xyz- wing pattern. this square is sometimes called a pivot or hinge. solving sudoku - xy- ...
100 Hard X-Wing Sudoku: Media, Clarity - Amazon.com
www.amazon.com
Practice your advanced sudoku-solving skills with these 100 hard sudoku puzzles , all of which will require you to use the X-wing solving technique in order ...
XY-Wing: Advanced Solving Sudoku Technique
www.createclassicsudoku.com
XY-Wing is a method used to refine the candiates of a square with multiple candiates. ... When one square with candidates {X, Y} is in the same row, column, ...
Irregular (W)XYZ-Wings : Advanced solving techniques
forum.enjoysudoku.com
As per my understanding, Irregular XYZ-Wings strategy is summarized as ... wings from what I understand from reading daily sudoku forums.
XY Wing - Sudoku Helper
sudoku.ironmonger.com
The XY Wing strategy uses three cells that contain two and only two candidates and have ... the XY Wing strategy is not related to the X Wing strategy.
Sudoku Solving Guide - SudoCue
www.sudocue.net
When you check the pattern for a digit, you may spot a set of locked candidates, alongside an X-Wing. Chances are slim that you stumble ...
Sudoku Puzzles by using x-wing techniques
oaji.net
The purpose of this essay is to implement and study different techniques for solving Sudoku puzzles, a problem similar to graph coloring with.
Basic & advanced Sudoku elimination techniques to solve ...
humage.com
Learn about solving Sudoku puzzles with various important techniques, such as X-Wing and Swordfish, all illustrated with clear pictures and detailed ...
Sudoku Fortschrittliche Lösungstechniken
www.janko.at
X-Wing, Swordfish, Jellyfish, Squirm Bag, Turbofish, Finned X-Wing, Sashimi Finned X-Wing ... This strategy works in the other direction as well.
omerfarukeker/Sudoku-Solver - GitHub
github.com
Solves the user entered Sudoku boards with commonly known strategies like hidden/naked pairs, X-wing, Y-wing etc. - GitHub - omerfarukeker/Sudoku-Solver: ...
Stuck at Sudoku? Here Are A Few Strategies To Get You ...
www.shawanoleader.com
This technique works with cells forming a rectangle, and it also occurs in rare situations. X-Wing is a pattern spanning multiple columns and ...
How to solve a Sudoku? - Telenet
users.telenet.be
A XY-Wing or XYZ-Wing with all cells in a same unit, is a naked triple with the values {X,Y,Z}. The next example shows how different solving techniques can be ...
How To Solve Sudoku Puzzles
puzzlebooksplus.com
Logic Techniques for Solving Sudoku ... You can use the X-Wing technique when a candidate number appears at all four corners of a rectangle, AND it is not a ...
XYZ - Wings - Speed Sudoku • View topic
www.speedsudoku.com
This is an extension of Y-Wing or (XY-Wing). John MacLeod defines one as "three cells that contain only 3 different numbers between them, ...
sudoku snake techniques
nkrafa.rtaf.mi.th
Sudoku X is played exactly the same way as the classic Sudoku, by filling in the numbers 1 through 9 in ... Sudoku Snake - Solving Technique - WXYZ Wings.
Finned X-Wing - Sudoku Solver
sudokusolver.app
In the sudoku diagram below, either in the R4C3 or R5C3 cells (marked in yellow) you can place the digit 6 or you have the X-Wing pattern, i.e. in the third ...
Please Give WXYZ Some Space | Systematic Sudoku
sysudoku.com
My early post on the regular XYZ-wing just passed “W” off as the rare ... with that in his Strategies page, presenting them as WXYZ-wings ...
Видео xyz-wing - imperiya.by
imperiya.by
Онлайн — Видео xyz-wing — imperiya.by. ... Advanced Solving Sudoku Technique - X-Wing ... Advanced Sudoku Strategy X-Wing Explained. ▻. RFC963 5 год.
X-Wing Strategy - SudokuWiki.org
www.sudokuwiki.org
Sudoku Strategy. X-Wings are the simplest of the chaining formations and are very easy to spot. They use four cells in a rectangle to make ...
X Wing - Learn Sudoku
www.learn-sudoku.com
An X Wing is a technique for removing candidates (pencil marks). It starts with either two parallel rows or two parallel columns.
Sudoku X-Wing technique: when and how to use
www.sudokuonline.io
Requirements to apply the Sudoku X-Wing strategy ... To be able to apply this technique, the player must find 2 rows or 2 columns where a single digit is a ...
Basic Fish (X-Wing, Swordfish, Jellyfish) - HoDoKu
hodoku.sourceforge.net
X-Wing ... Take two rows (the base sets). If you can find two columns, such that all candidates of a specific digit (the fish digit) in both rows are containd in ...
X-Wings – Sudoku of the Day
www.sudokuoftheday.com
Solving Sudoku : X-Wings ... X-Wings are fairly easy to spot, but a little harder to understand than some other techniques. Like others it relies on using ...
X Wing - Sudoku
www.livesudoku.com
X Wing Tutorial · X Wing · It happens to be that those 4 cells (2 in each row) align up perfectly in the same two columns - column 5 and column 7. · This is called ...
X Wing - Sudoku Beginner
www.sudokubeginner.com
X Wing is an advanced sudoku technique, which means that the end result will not necessarily be finding the number that goes in a cell.
Sudoku X Wing Technique with Examples
sudoku.com.au
Sudoku X Wing Technique with Examples · Consider any one candidate · Consider any two distinct rows · Let the candidate be limited to no more than two cells in ...
X-Wing Strategy - Sudoku - Thonky.com
www.thonky.com
X-Wing is a strategy in which you find a candidate that appears twice in two different rows, and those appearances are both in the same ...
X-Wing - Rätselagentur Simon
www.thinkgym.de
Am folgenden Beispiel möchten wir Ihnen eine Situation erläutern, in der wir die Sudokustrategie des X-Wing anwenden. Die schwarzen Zahlen sind die ursprünglich ...
Solving Technique - Finned X Wings - Sudoku Snake
www.sudokusnake.com
A Finned X-Wing is a pattern that is one cell short of being an X-Wing - in other words, two columns that contain a candidate in only two rows, ...
Sudoku Strategy. X-Wings are the simplest of the chaining ...
www.pinterest.co.uk
X-Wing Strategy. Sudoku Strategy. X-Wings are the simplest of the chaining formations and are very easy to spot. They use four cells in a rectangle to make ...
Sudoku Puzzles by using x-wing techniques
oaji.net
With many advanced techniques, the key is to spot patterns within your pencil marks to eliminate possibilities within other squares. The x-wing technique:.
Sudoku Solving Techniques
www.sudoku.org.uk
Y-Wing Strategy. This is an excellent candidate eliminator (and is also known as XY-Wing). The name derives from the fact that it looks like an X-Wing - but ...
X-Wing - Sudoku Solving Techniques
sudoku9x9.com
X-Wing ... If a digit is a candidate for exactly two cells in two different rows and the positions (columns) of those two cells in those two different rows are ...
Sudoku Help - X-Wing - BrainBashers
www.brainbashers.com
An X-Wing is a advanced technique which can eliminate certain candidates from squares. Its name comes from the pattern formed by the digits. We are looking for ...
Sudoku X Wing Practice - Advanced Sudoku Strategy Finned ...
jorjabartlett.blogspot.com
Sudoku Puzzles By Using X Wing Techniques Logic Teaching Mathematics from imgv2-1-f.scribdassets.com This strategy is looking at single numbers ...
Sudoku Solutions, Advanced- X-wing, XY-Wing, Swordfish
www.puzzles-on-line-niche.com
mentioned solution types. X-Wing. To solve Sudoku puzzles using this process, one must have recognition of number relationships.
X-Wing Sudoku Solving Techniques
sudokuswami.com
The X-wing pattern appears in tricky sudoku puzzles when two rows or columns contain just two cells that hold matching candidates.
Sudoku Sashimi Finned X-Wing Strategy explained
www.taupierbw.be
Sudoku strategies explained with graphics. ... Sashimi Finned X-Wing. If a particular candidate is present in only two Cells in a Row and if you can find ...
X-wing (Sudoku) - — Wikipédia
fr.wikipedia.org
La méthode X-Wing est une technique de résolution de Sudoku. Son nom provient des X-wing de Star Wars, le X fait référence à la disposition des cases ...
X-Wing - Solving sudoku strategy
www.sudoku9981.com
Introduce sudoku solving technique : An X-Wing is a fish pattern involving 2 rows and 2 columns.It is a single-digit solving technique that allows the ...
X Wing and Other Fishy Things - Sudoku Helper
sudoku.ironmonger.com
Sudoku Helper - HowTo for Sudoku solving technique fishyThings. ... The X Wing strategy looks for two rows that only have two instances of ...
This Sudoku Actually Teaches The X-Wing Technique!
iam.t-rkr.de
This Sudoku Actually Teaches The X-Wing Technique! Upload: 29 10 2020 10:07. Tags: sudoku. Source Gelöst in 59:49 ...
raphael-kahler/SudokuSolver: Apply common sudoku solving ...
github.com
Sudoku Solver. A solver for Sudoku puzzles that uses common solving techniques. The solver shows for every step which technique was used, so you can follow ...
Sudoku difference between x wing and double pair - Puzzling ...
puzzling.stackexchange.com
Double Pairs and X Wing are listed as different techniques here (former is a medium and later a master technique). The only difference I can see ...
Su Doku puzzle needing x Wing technique, can anyone help?
forum.enjoysudoku.com
I was recommended to use X Wing which I am totaly unfamiliar with. I looked at SadMan Software ... http://www.sadmansoftware.com/sudoku/.
Sudoku Puzzles 129 - Associated Pairs, X-Wing
www.sudoku129.com
Solving methods > 4- Complex methods > 4.1 Associated pairs (X.wing). The following methods are not necessarily more difficult to understand that the above ...
How to solve hard Sudoku puzzles
minimindgames.com
Here are the most common techniques to solve hard Sudokus. X-wing. X-wing. If a candidate appears in two columns (rows) in exactly ...
JSudoku - Fishes & Single Digit Techniques
jcbonsai.free.fr
This is a generalization of the X-Wing, Swordfish, Jellyfish which is more frequent is some variants like Diagonal Sudoku. It is based on strong links and uses ...
Sudoku Puzzles by using x-wing techniques - Academia.edu
www.academia.edu
International Journal of Computer TechniQues - Volume1 Sudoku Puzzles by using x-wing techniques Dr. Zubair Khan1, Ashish Kumar2, Sunny Kumar3 M.Tech ...
X-Wing - Sudoku technique
www.free-sudoku-puzzle.net
An X-Wing can also occur on 3 rows or columns instead of 2. This is called a SwordFish. Install Free-Sudoku-Puzzle as an app.
How to solve a Sudoku? - Telenet
users.telenet.be
5. X-Wing. When there are only two possible cells for a value in each of two different rows, and these candidates lie also in the same ...
Solving Sudoku - Angus Johnson
www.angusj.com
Rules and hints for solving Sudoku puzzles. ... The X-Wing and Swordfish techniques can be further generalised to include rows containing candidates ...
Sudoku Solving Techniques - Kristanix Games
www.kristanix.com
Tips on Solving Sudoku Puzzles - Sudoku Solving Techniques ... X-Wing. This method can work when you look at cells comprising a rectangle, such as the cells ...
Sudoku Assistant -- Solving Techniques - St. Olaf College
www.stolaf.edu
Other advanced techniques are required to solve more difficult Sudoku puzzles ... (An X-wing is really a naked pair; a swordfish is a naked triple, etc.) ...
Sudoku Strategy Tips, Tutorials and Videos
www.eadvancedsudoku.com
With step-by-step Sudoku strategy tips, tricks and video tutorials. ... The X Wing method is a way to help you solve very hard Sudoku puzzles!
Aftermath of October 31 meeting - UCI Math
www.math.uci.edu
A Practice Sudoku Puzzle (from "Enjoy Sudoku" LEARN X-Wing) (image1) ... A puzzle solvable using only basic techniques (Puzzle 71 in Chapter 7 of Gordon) ...
Sudoku techniques - Conceptis Puzzles
www.conceptispuzzles.com
The X-Wing technique is used in rare situations which occur in some extremely difficult puzzles. Scanning column a we see that 4 can only be in square a2 or ...
X Wing 数独Sudoku - 程序猿
www.wjhsh.net
An X Wing is a technique for removing candidates (pencil marks). It starts with either two parallel rows or two parallel columns. Blocks are not involved here.