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Sudoku Forums

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Sudoku Xtra forum
Fairly busy forum with discussion of all aspects of Sudoku and related puzzles, as well as the monthly Sudoku Xtra magazine.
YouPlay! Forums
Engage with a community of dedicated Sudoku enthusiasts via specialty forums and site-wide chat. You can even get in touch with the Sudoku generator and site developers.
Sudoku Players' Forums
Originally the most active Sudoku forum, started by Wayne Gould, but currently owned by RealNetworks, Inc. Many new solving techniques were developed by its members but were lost in a server failure - see the following entry.
New Sudoku Players' Forum
Created from a 2009 backup of the original Players’ Forums by concerned members when it crashed in 2010. Over 70,000 postings were recovered including those covering the development of many major techniques. The forum is still live.
Sudoku Programmers
A forum where programmers exchange ideas about writing Sudoku computer programs. Not as active as it used to be, but still a considerable resource for finding solving techniques. This forum is also used by Angus Johnson as a support forum for his Simple Sudoku program.
Sudoku Discussions
This forum was founded by the late Mike Mepham. It is currently managed by Andrew Stuart, who supplies the Sudokus for the Daily Telegraph in the UK and the LA Times. The Eureka board has very lively discussions that explore the uncharted territories of the Sudoku world.
SudoCue Users
A forum hosted by Ruud, the author of SudoCue and SumoCue. An excellent place to learn how to solve extremely difficult Sudokus and several Sudoku Variations. It has a very active Killer Sudoku community.
Daily Sudoku
A forum for the Daily Sudoku website, hosted by Sam Griffiths-Jones.
DJApe - The Home of Perfect Sudoku
A forum hosted by DJ-Ape, the author of Perfect Sudoku. A perfect place to discuss the Killer Sudoku variant.
Sudoku Assistenten Forum
A forum hosted by Havard, one of the authors of the Sudoku Assistenten program. Includes threads for support, sharing sudokus and advanced techniques.
Sudoku Puzzles - Sudoku Tips
Frequent tips and illustrated puzzle proofs by Steve K, as well as discussion between the various members.
SudokuSolver Forum
Hosted by R.C. Broughton, author of the SudokuSolver program. A forum for Sudoku enthusiasts to share puzzles, techniques and software.

Dutch

SudokuPlaats forum
A small but clean forum to discuss Sudoku and off-subject matter in Dutch.
Players & Programmers forum
The administrator has left the building. Spammers have taken over the forum.

Vietnamese

sudoku.vn

Online Daily Sudoku Puzzles

Ordinary Sudoku

BrainBashers Sudoku
Daily sudokus with six levels of difficulty. The list of solving techniques needed for their puzzles are listed here. Solutions to each puzzle includes a walkthrough. The archive dates back to 2005 January 1.
Sudoku XL
Millions of sudoku to be played online or printed. High score function and the possibility to print several sudoku per printed page. Levels that suits both beginners and more advanced sudoku solvers.
Daily Sudoku Puzzles
A free online sudoku with built in solver.
Sudoku Tips
Tips and strategies to solving sudoku.
Free Sudoku
Contains a free sudoku game download, daily sudoku and printable sudoku puzzles.
Sudoku Center Online
9 sudoku puzzles of 5 different levels. You can find Sudoku Solver too.
YouPlay!
Free puzzle website created by Lovatts Publications, leaders in the field of puzzle production. This site has Sudoku to suit all playing levels, a site-wide chat room and a growing community of Sudoku enthusiasts.
Fed-sudoku
3 clasic sudoku puzzles and one nonconsecutive sudoku puzzle daily and many sudoku variants, everything online and with many scoreboards and statistics. (Slovak and English versions)
Sudoku.com.au
9 sudoku puzzles daily, all free. A great online player, but the biggest drawcard is the huge active community which is very friendly. They have lots of online helpers, as well as blank printable sheets and a sudoku blog which gives out daily solving tips.
The Daily Nightmare
A daily puzzle from the creator of SudoCue which more than lives upto its name. Not for the faint hearted - as the full arsenal of solving techniques is required. The puzzle's archive dates back to December 2005.
One Trick Pony
A daily puzzle from the creator of SudoCue which requires a good range of solving techniques, plus one advanced step to solve. The puzzle's archive dates back to November 2006.
The Daily Lite
Four new puzzles everyday, from the creator of SudoCue, of four levels of difficulty. Ideal for developing and enhancing solving techniques.
Times Online - Sudoku
The London Times. Two daily puzzles of different levels of difficulty. The most advanced techniques required to solve the hardest (Super Fiendish) Times daily puzzles are X-Wings, Naked Subsets and Hidden Subsets. Upto seven days of archived puzzles. Links to recent Sunday Times puzzles and published Times supplement collections.
Sudoku.org.uk
A daily Mike Mepham puzzle of varying levels of difficulty. The hardest puzzles, the Diabolical and the weekly Extreme, require a wide range of solving techniques. A thirty day puzzle archive. The site also publishes daily Jigsaws and Killers.
Daily Mail (uk) - Sudoku
Two daily puzzles of different levels of difficulty. The most advanced techniques required to solve the hardest (Diabolical) daily puzzles are Naked Subsets and Hidden Subsets. The puzzle archive dates back to 2005 October 8.
Guardian Unlimited (uk) - Sudoku
A daily puzzle of varying levels of difficulty (Mon to Sat). The most advanced techniques required to solve the hardest (Hard) daily puzzles are Naked Subsets and Hidden Subsets. The puzzle archive dates back to May 2005.
The Daily SuDoku
A daily Sudoku with difficulty varying from easy to very hard. The archive goes back to January 2005. 3 Sudoku Variations are also published daily.
playr.co.uk/sudoku
Daily sudokus by Gaby Vanhegan with six levels of difficulty. The hardest puzzles have at least Nightmare standard. The archive goes back to 2005 October 10.
7star Sudoku
Mostly daily symmetrical sudokus which occassionally require the most advanced techniques. The archive dates back to 2006 May 1.
Online Picture Sudoku
Sudoku puzzles with pictures (numbers also available) playable online and generated at random each time the page is loaded. All can be solved with more simple techniques, and have only one solution. You can put Sudoku on your own site with your own pictures.
Free Sudoku Games
Play free sudoku games online or just download the pdf containing the puzzle and play offline.
Kodden's Daily Sudoku
A new sudoku puzzle every day and randomly generated puzzles of various difficulty.
Sudoku puzzles for beginners
Free on-line Sudoku game that offers assistance in finding the correct solution. Solve one of the included puzzles or enter your own.
Sudoku By Zol
Free unlimited puzzles: 5 difficulty levels. Unique efficient user interface, especially for Pencil Marks. Enter your own puzzles and solve them yourself online. All puzzles are printable puzzles. Become a fan on the Sudoku By Zol Facebook Page.
PuzzleMix
With new puzzles online every day, and thousands of active solvers, PuzzleMix features Sudoku at a range of sizes and difficulties for online play, complete with a wide range of intelligent solving assistants
Sudoku Snake
An extensive website containing explanations of over 40 solving techniques, daily printable puzzles at 9 different difficulty levels, and other sudoku information.
Online sudoku game
Free online sudoku for all players from kids (4x4 board with flowers) to most experienced (program offers mode with automatic "pencil marks" and other features that helps to solve difficult sudoku puzzles). Requires Java.
Fishy Sudoku
Not for beginners! New puzzles daily require X-Wing, Y-Wing and the occasional Swordfish. Great interface, automatic (but still editable) pencilmarks. Hints engine helps you when you get stuck. Complete archive available. Play on facebook.
Mister Sudoku
An extensive collection of sudoku puzzles with a wide variety of types (Standard / Jigsaw / Killer), sizes and difficulties. Hints engine helps if you're still learning or simply stuck. Also includes a variety of scoreboards which track your performance globally, nationally and amongst your Facebook friends. Play on facebook.

Online Sudoku Puzzle Collections

Ordinary Sudoku

Pure Sudoku - Printable Sudoku Puzzles
A collection of printable sudoku puzzles at 5 difficultly levels.
New Sudoku Players’ Forum
Has many different puzzle collections in the General/puzzle forum. A good place to start is the Puzzle collections sorted by solving qualities.
SudoCue Downloads
Has 7 download Sudoku files available, for the SudoCue Program. The puzzles collections are aimed at all different levels of playing ability. nb Beginners should start with The Learning Curve Collection.
Sudoku Assistenten forum - Share sudokus
A collection of interesting and difficult puzzles posted by the forum's members.
Web Sudoku
A different puzzle is presented for each log in. It is also an online puzzle generator, where the level of difficulty (four levels) is chosen by user. It appears that the most advanced technique that is required to solve the hardest Web Sudoku puzzles (Evil) are Naked Subsets and Hidden Subsets.
Minimum Sudoku
Contains 36628 distinct starting grids with 17 givens. (Currently, it is believed that at least 17 givens are needed to construct a valid puzzle.)
Sudoku puzzles
Puzzles are divided into eight difficulty levels.
Color coded sudoku puzzles
Free online color coded sudoku puzzle solver with timer, pencil, graph, hints, multiple difficulty level etc
Razzle
Free online/printable sudoku puzzles ranging from easy to expert. Expert level requires X-Wing, XY-Wing, Simple Colouring, and Swordfish techniques to solve.

Terminology

From Sudopedia (Note: the links in this section are disabled)

The Sudoku community has developed its own terminology. Most of the basic terms are now widely accepted, but some concepts are known by many different names. Here is an alphabetic list of the most commonly used terms.

0-9

3D Medusa
A coloring technique for multiple digits.
45 rule
A rule stating that the sum of the cells in a house must be 45. This is most applicable to Killer Sudoku.

A

Advanced Coloring
An alias used for 3D Medusa.
AIC
An acronym used for Alternating Inference Chain.
Aligned Pair Exclusion
A solving technique that examines the possible configurations for a pair of cells in an intersection.
Aligned Triple Exclusion
A solving technique that examines the possible configurations for a triple of cells in an intersection.
Almost Locked Set
A set of N cells with candidates for N+1 digits.
ALS
An acronym used for Almost Locked Set.
Alternating Inference
See: Inference
Alternating Inference Chain
A chain with alternating strong and weak inference.
APE
An acronym used for Aligned Pair Exclusion.
Ariadne's Thread
A metaphore used for backtracking.
Asymmetric Puzzle
A puzzle is asymmetric if its particular geometric shape is such that rotations or reflections do not result in the same bit pattern of clues. Essentially all of the different digits in the clue are converted into a single bit which is on if the clue for that position was given and off if there is no clue for that position.
ATE
An acronym used for Aligned Triple Exclusion.
Automorphic solution grids
 ??

B

B/B Plot
A diagram showing strong links.
Backdoor
Placement of a digit from the solution into a cell which reduces the difficulty level of the remaining puzzle.
Backtracking
Return to an earlier position in the solving path, after a contradiction or a dead end has been reached.
Band
An alias used for floor.
Bifurcation
A limited form of Trial & Error where only constraints with 2 remaining candidates are considered.
Big Number
Collective term for given and placed digits, as opposed to little number for pencilmarks.
Bilocal Unit
A unit constraint with only 2 candidates left.
Bivalue Cell
A cell with only 2 candidates left.
Bivalue Universal Grave
A pattern in which all cells have 2 candidates, which causes the Sudoku to have 0 or 2 solutions.
Block
An alias used for box.
Block-Block Interaction
An alias used for Locked Candidates type 2.
Bowman Bingo
A solving technique that does a systematic analysis of all implications for a move.
Box
A group of 9 cells in a 3x3 formation. In a Sudoku grid, boxes usually have a thicker border.
Box Exclusion
A method by which hidden singles can be found by excluding candidates within a box using non-duplication with rows and columns; an alias for cross-hatching
Box-Line Reduction
An alias used for Locked Candidates type 2.
Boxcol
The intersection of a box and a column.
Boxrow
The intersection of a box and a row.
Braid Analysis | Braiding
A solving technique that analyzes the way digits are organized in a chute.
Bridge
A weak link that connects 2 clusters in a coloring technique.
Broken Wing + Guardians
A solving technique that uses Turbot Fish patterns and Guardians to make eliminations.
Buddy
An alias used for peer.
BUG
An acronym used for Bivalue Universal Grave.
BUG Lite
A deadly pattern that is between Unique Rectangle and BUG.

C

Cage
Isolated part of the grid in a Killer Sudoku, with the sum of all caged cells in the top left corner.
Candidate
A possible digit that may be placed into a cell. Candidates are represented by pencilmarks.
Candidate elimination cell
A cell that contains a candidate capable of causing a contradiction in a fish pattern.
Canonical Form
A standard form of presentation which will identify if two puzzles are scrambled duplicates.
Cell
A small square in a Sudoku grid that can contain a single digit.
Cell Set
An alias used for house.
Chain
A series of linked cells or candidates.
Chute
A part of the grid which is either a floor or a tower.
Claiming
An alias used for Locked Candidates type 2.
Clue
An alias used for given.
Cluster
A group of candidates which are all interconnected with strong links. Used in Coloring.
Column Exclusion
A method by which hidden singles can be found by excluding candidates within a column using non-duplication with rows and boxes; a process similar to cross-hatching but within a column.
Color Trap
A coloring technique that eliminates candidates outside a single cluster.
Color Wing
A coloring technique that eliminates candidates using multiple clusters.
Color Wrap
A coloring technique that eliminates candidates inside a single cluster, by means of contradiction.
Coloring
A solving technique that uses colors to identify conjugate pairs. Can be simple (single or one chain) or multi- (two chains). Also described as Magnetism by some authors.
Column
A vertical line in the grid, containing 9 cells.
Common Peer Elimination
If all cells in a particular constraint contains a particular digit as a candidate sees another cell, then that digit can be eliminated from the latter cell. This is a basic technique used in Sudoku Variations with irregular groups of cells.
Conflict
An alias used for contradiction.
Conjugate pair
The last 2 candidates for a particular digit in a single house. Used in Coloring.
Connected pair
A pair of candidates which cannot both be false at the same time.
Constraint
A restriction derived from the rule. Sometimes used as an alias for house.
Contradiction
The state of the grid in which the puzzle no longer complies with the rule.
Cross-Hatching
A method by which hidden singles can be found.
Crossover
A basic technique for Sudoku-X, which looks at eliminating common peers of diagonal cells.

D

Deadly Pattern
A pattern that would cause a Sudoku to have multiple solutions.
See also: Unavoidable Set
Diagonal
A group of 9 diagonally connected cells. In Sudoku-X and other variants, the diagonals must also contain digits 1 through 9.
DIC
An acronym used for Double Implication Chain.
Digit
A number between 1 and 9 which can be placed into a cell.
Disjoint Subset
An alias used for subset.
Division
A method by which the cells in the grid are divided into 9 houses. All rows together form a division and so do all columns and all boxes.
Double Implication Chain
A chain that propagates implications in both directions.

E

Eliminate
Removing a candidate from the grid.
Empty Rectangle
A solving technique that uses a strong link and grouped candidates.
Equivalence Marks
A solving technique that uses marks to represent parity instead of colors.
See also: GEM | Graded Equivalence Marks
Equivalent
A term which indicates that a group of candidates must be true or false together.
ER
The acronym for Empty Rectangle.
Error
An alias used for contradiction.
Eureka | Eureka notation
A notation system for chains and loops.
Exclusion
The process of removing a candidate from the grid

F

Family
An alias for peer
Fillet-O-Fish
See: Finned Fish
Fin
The additional candidate(s) in the box constraint that belongs to a Finned Fish
Finned Fish
A variety of fish that uses an additional box constraint.
Fish
A set of solving techniques that compares sets of unit constraints for a single digit.
Fishy Cycle
A loop formed by candidates for a singe digit.
See also: Turbot Fish
Fixed Digit | Number | Value
An alias used for given.
Floor
A part of the grid containing 3 rows and 3 boxes.
Floor Minlex
A minlex of a floor. There are 416 possible floor minlexes.
Forced Digit
An alias used for Naked Single.
45 rule
A solving technique in Killer Sudoku making use of the knowledge that the digits in each house add to 45.
Franken Fish
A variety of fish that uses multiple additional box constraints.
Full House
A house with only a single empty cell.

G

Gattai
A puzzle with 2 or more overlapping Sudokus.
GEM
An acronym used for Graded Equivalence Marks
Given | Given Digit | Given Number
A digit placed in a cell by the puzzle setter. It cannot be changed by the player.
Graded Equivalence Marks
A solving technique that uses marks in the pencilmark grid to represent different grades of parity.
See also: Equivalence Marks
Gerechte Design
A special design of a Latin square where the n × n Latin square grid is also divided into n regions, with n cells in each.
Grid
81 cells organized in 9 rows and 9 columns.
Group
An alias used for house.
Guardian
See: Broken Wing
Guess
A digit placed into a cell without a logical reason.

H

Hatching
An alias used for Cross-Hatching.
Hidden Single
A unit constraint with only a single candidate remaining. The digit can be placed in the candidate's cell.
Hidden Subset - Hidden Pair | Hidden Triple | Hidden Quad
A solving technique that isolates a group of cells and digits from the remainder of a house.
Hinge
An alias used for Empty Rectangle.
Hint
An alias used for given.
House
A group of 9 cells that must contain digits 1 through 9. A house can be a row, a column or a box in standard Sudoku.

I

Implication
Effect on a candidate caused by the true or false state of another candidate.
Improper puzzle
An alias used for invalid.
Inference
Interaction between the true or false states of 2 linked candidates.
Initial Digit | Number | Value
An alias used for given.
Innie
In Killer Sudoku, a cell that does not belong to any of the selected cages, but lies inside the tested house(s).
Innie-outie difference
In Killer Sudoku, the difference between the innies and outies may be used to eliminate candidates.
Intersection
A part of the grid where 2 houses share one or more cells. Mostly used for intersections between a box and a row or column.
Intersection Removal
An alias used for Locked Candidates.
Invalid
A Sudoku is invalid if it has no solutions or multiple solutions.
Irreducible puzzle
An alias used for Minimal Puzzle
Isomorphic Puzzles
Two puzzles (puzzles or solution grids) are isomorphic if they can be converted into one another through renumbering or allowed geometrical transformations. There are 6,670,903,752,021,072,936,960 different solution Sudoku grids, but only 5,472,730,538 of these grids are unique. Thus there are on average about 1.218 x 10^12 isomorphic Sudoku solutions per unique solution.

J

Jellyfish
A fish of size 4.
Jigsaw
A Sudoku variant that has irregularly shaped regions.

K

K9
A way to reference Sudoku cells, by using a letter for the row and a number for the column.
Killer | Killer Sudoku
A Sudoku variant where givens are replaced by cages labeled with the sum of the digits to be placed inside them.
Killer Convention
In Killer Sudoku, the convention that all digits in each cage is distinct.
Killer Subset
An extension of the Subset technique that is applicable to Killer puzzles.
Kraken Fish
A fish pattern with indirect connections to a candidate which can be eliminated.

L

Last Digit
The last placement of a digit.
Last Value
 : An alias used for Last Digit
Law of Leftovers
A solving technique used for jigsaw Sudokus.
Line
A house that is either a row or a column.
Line-Box Interaction
An alias used for Locked Candidates.
Link
Connection between 2 cells or candidates. See also: Strong link and Weak link.
Little Number
An alias used for pencilmark.
Locked Candidates
A solving technique that uses the intersections between lines and boxes.
Locked Pair
A Naked Pair located in a single intersection.
Locked Triple
A Naked Triple located in a single intersection.
Locked Set
An alias used for subset.
LoL
An acronym used for Law of Leftovers
Loop
A loop of linked cells or candidates.

M

Magic Cell
An alias used for backdoor.
Mark | Markup
An alias used for pencilmark. Also the act of placing them in the grid.
Mathematically equivalent
Puzzles which are essentially the same. By permutating rows, columns and digits, one can be mapped to the other.
Maximal
A puzzle is maximal if it has the maximum number of clues possible, and yet there is a unique solution. In a game on a NxN grid, then the maximum number of clues is N^2-3.
MC
An acronym used for Multi-Colors
Mini-col
An alias used for boxcol.
Minimal
A puzzle P is minimal if it has one and only one solution and if every given is necessary. In other words, if any one of the givens is deleted, then the puzzle obtained has more than one solution.
Mini-row
An alias used for boxrow.
Minlex-Puzzle
?
Multi-Colors
A coloring technique that uses more than 2 colors, forming multiple clusters.
Mutant Fish
A fish pattern with an odd mixture of rows, columns and boxes.

N

Naked Single
A cell with only a single candidate remaining. It can be placed in the cell.
Naked Subset - Naked Pair | Naked Triple | Naked Quad
A solving technique that isolates a group of cells and digits from the remainder of a house.
Nishio
A limited form of Trial & Error where only candidates for a single digit are considered.
Node
A cell in a chain or loop.
Nonet
An alias used for box. This is the preferred term for Killer Sudoku.
Number
An alias used for digit.

O

Opposite | Opposite Parity
Different parities in a single cluster. Only one of them can be true.
See also: Conjugate pair
Orbit
A group of cells which must all contain a given or be empty in order to preserve symmetry.
Outie
In Killer Sudoku, a cell that belongs to one of the selected cages, but lies outside the tested house(s).

P

Parity
Status of a candidate relative to other candidates. Parity is represented by a color or parity mark.
Pattern Overlay Method
A solving technique that examines possible ways to place remaining candidates in the grid.
Peer
A cell that shares a house with another cell.
Pencilmark
The representation of a candidate.
Pincer
One of the end cells in an XY-Wing or XYZ-Wing.
Pinned Digit
An alias used for Hidden Single.
Pivot
The central cell in an XY-Wing or XYZ-Wing.
Placement
Placing a candidate into an unsolved cell, thus changing it to a solved cell.
PM
The acronym for pencilmark.
Pointing Pair
An alias used for Locked Candidates.
POM
An acronym used for Pattern Overlay Method
Possibility
An alias used for candidate.
Proper puzzle
An alias used for valid.
Puzzle
Any incomplete Sudoku grid which follows the One rule. There may be one or more solutions.

R

Random Puzzle
For any given computer program which creates puzzles, a random puzzle essentially is a puzzle which is created chaotically, that is to say so randomly that the created puzzle would never (for all practical purposes) be created again.
Reducible puzzle
An alias used for a Proper puzzle
Region
An alias used for box.
Remaining Possibilities
An alias for candidate
Remote Pair
A solving technique that combines several Naked Pairs.
Restricted common
A digit which cannot be present in 2 Almost Locked Sets at the same time.
rncn
A way to reference Sudoku cells, by using a row number and a column number.
Rookery
A term for the pattern of 9 cells that a one digit could occupy in a completed Sudoku grid. A k-Rookery would be the pattern of cells that k-digits could occupy.
Row
A horizontal line in the grid, containing 9 cells.
Row Exclusion
A method by which hidden singles can be found by excluding candidates within a row using non-duplication with columns and boxes; process similar to cross-hatching but within a row.
Row Minlex
A row minlex is a particular canonical form which represents the set of isomorphic solution grids. It has the first row as the digits 1-9 in sequence, hence the name (see wiki page for more details).
Row/Column-Block Interaction
An alias used for Locked Candidates type 1.
Rule
The one rule of Sudoku. Complete the grid in such a way that each row, column and box contain digits 1 through 9.

S

Samunamupure
Alias for Killer Sudoku. It is the Japanese form of "sum number"
Samurai
An variant with 5 overlapping Sudokus in an X pattern.
Sashimi Fish
A variety of fish where not all defining candidates are present.
SC
An acronym used for Simple Colors
Scramble
Create a mathematically equivalent grid from a given grid.
Seafood | Sealife
Aliases used for Fish.
See
Two cells see each other if they belong to the same constraint (row, column or box).
Sector
An alias used for house.
Segment
An alias used for intersection.
Set
An alias used for house.
Shaolin
A Gattai-25 Sudoku variant with 36 overlapping boxes.
Shi Doku
A NxN Sudoku variant played with a 2x2 box. Thus the grid is 4x4 and the digits 1-4 can be used.
Simple Colors
A coloring technique that is limited to 2 colors, using a single cluster.
Single
Elementary solving technique, using the fact that only a single candidate is left for a constraint.
Skinny Fish
See: Sashimi Fish
Skyscraper
A particular variety of Turbot Fish.
Solution
The answer to the puzzle. A grid where each cell contains a digit between 1 and 9 without violating the rule.
Solving path
A list of steps that shows how a particular puzzle is solved.
Square
An alias used for cell.
Squirmbag
A fish of size 5.
SSTS
Simple Sudoku Technique Set. The set of techniques supported by the Simple Sudoku program.
Stack
An alias used for tower, sometimes used as an alias for boxcol.
Strong Inference
see: Inference
Strong link
A link caused by a bivalue cell or bilocal unit.
Subgrid
An alias used for box.
Subset
Usually refers to Naked Subset or Hidden Subset.
Sudoku
A puzzle defined by a grid with givens and a unique solution, which can be found by completing the grid according to the rule.
Sudoku-X
A Sudoku variant where every diagonal must also contain the digits 1 to 9.
Subset
A set formed by N cells and N digits, which are or can be isolated from the remaining cells and digits in a house.
Sumo
A Gattai-13 Sudoku variant with 16 overlapping boxes.
Swordfish
A fish of size 3.
Symbol
An alias used for digit.
Symmetric Puzzle
A puzzle is symmetric if its particular geometric shape is such that rotations or reflections result in the same bit pattern of clues. Essentially all of the different digits in the clue are converted into a single bit which is on if the clue for that position was given and off if there is no clue for that position.

T

Tabling
A form of Trial & Error where all candidates are tried.
Target Cell
A cell selected for analysis of remaining possibilities.
Target Number
A number selected for analysis using techniques that seek to find the location of the number within a group.
Tower
A part of the grid that contains 3 columns and 3 boxes.
Traveling Pairs
An alias used for Braid Analysis.
Trebor's Tables
An alias used for tabling.
Trial & Error
A solving technique that eliminates candidates by proving that their placement leads to a contradiction.
Turbot Fish
A solving technique that uses loops of odd length for a single digit.

U

Unavoidable Set
A group of cells in the solution grid that requires at least one given.
Unique Rectangle
An Unavoidable Set with a rectangular shape.
See also: Deadly Pattern
Unique Solution
The assumption that a Sudoku has a single solution. Subject of debate, especially when used in solving techniques.
Uniqueness Test
A series of solving techniques in which the solver avoids Unique Rectangles.
Unit
An alias used for house.

V

Valid
A Sudoku is valid if and only if it has a unique solution.
Value
An alias used for digit.
Veracity
See: Verity.
Verity
A statement which is true for all alternatives in a limited set.

W

Walkthrough | Walkthru
An alias used for Solving path.
Weak Inference
see: Inference
Weak link
A link between 2 peers or 2 candidates in a single cell.
Windoku | NRC-Sudoku
A Sudoku variant with 4 extra "windows", and each window must also contain the digits 1 to 9.
WXYZ-Wing
An extension of XYZ-Wing to 4 cells.

X

X-Cycle
A loop containing candidates for a single digit.
See also: Fishy Cycle
X-Wing
A fish of size 2.
XY-Chain
A chain of cells with 2 candidates each.
XY-Wing
A short XY-Chain with only 3 cells.
XYZ-Wing
A variation of XY-Wing that has an extra candidate in the pivot cell.
XYZW-Wing
Alias for WXYZ-Wing.

Y

Y-Wing
An alias used for XY-Wing.


 

 

 

Sudoku Guides

It should be noted that a number of guides are a bit dated. For the newest developments of Sudoku techniques, please see the Sudoku forums.

Online

Guides that are available online for free.

Ordinary Sudoku


 

Killer Sudoku

Books

 

 

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