Glossary

(Bookkeeping Tactic)

A Unique Rectangle with a Hero or Heroes in only one of its Cells.

It is immediately exploitable.

See Unique Rectangle.

(Bookkeeping Tactic)

A Unique Rectangle with Heroes in two of its Cells that are diagonally opposite.

Sometimes exploitable with Chains.

See Unique Rectangle.

(Bookkeeping Tactic)

Row-Based 2-Fish in 9:

• Two Rows have Twin 9s.
• These 9s happen to be framed in two Columns.
• You can kill all the other 9s in the two Columns.

(Similar remarks for a Column-Based 2-Fish.)

See 2-Fish.

(Bookkeeping Tactic)

A Unique Rectangle with Heroes in two of its Cells that are adjacent to each other.

Sometimes exploitable with Chains.

See Unique Rectangle.

(Bookkeeping Tactic)

A Unique Rectangle with Heroes in three of its Cells.

Sometimes exploitable with Chains.

See Unique Rectangle.

(Bookkeeping Tactics)

Row-Based 3-Fish in 9:

• Three Rows have Twin or Triplet 9s.

• These 9s happen to fall in exactly three Columns, where each of the Columns contains at least two of these 9s.

• You can kill all the other 9s in the three Columns.

3-Fish are not easy to spot.

(Similar remarks for a Column-Based 3-Fish.)

See Other Fish.

(Bookkeeping Tactic)

This is an Attack Chain.

A 3-Pair-Cell Chain is an Aimless Chain consisting of three Pair Cells that will kill some specific candie-value in the Cells in its Target Area (if the candie-value occurs).

See Chain.

(Bookkeeping Tactic)

A Unique Rectangle with Heroes in all four of its Cells.

Rarely exploitable.

See Unique Rectangle.

6-Cell Flip-flop+n

(Bookkeeping Tactic)

A 6-Cell Flip-flop+n is a recognizable pattern that would be a Flip-flop if it weren't for the presence of extra candies called Heroes in n of its Cells.

There are applicable Tactics, often involving Chains.

See Unique Rectangle.

• Scanning:  A Cell will accept a digit if none of the Cell's Buddies contain that digit as a BigNum.

• Bookkeeping:  A Cell will accept a digit if the (updated) list of candies in the Cell contains that digit.

• If a Cell will accept several different digits, then you don't yet know which of those will turn out to be the BigNum in that Cell.

Almost Deadly Pattern

An Aimless Chain is an Attack Chain of very simple form that you notice on the Grid.  The Chain can kill some specific candie-value in the Cells in its Target Area, but the desired victims may or may not exist.

(Opposite of Directed Chain.)

See 3-Pair-Cell Chain, Little ALS Chain, and Same-Pair Chain

See Chain.

For two or three identical candies in a Block:

Two or three 9-candies are aligned if they lie in the same Bandit or in the same Twit.

(The opposite of aligned is oblique.)

See Claim.

BUG+n

An Almost Claim in 9 is a group of Cells (in one House) containing 9-candies which would constitute a Claim in 9 if it weren't the presence of one or more 9-candies in some other Cell(s) of that House.  If some move eliminates the other 9-candie(s), then the original group will now become an actual Claim.

The idea of an Almost Claim is specifically useful as a component of a Gotcha Chain or a Wrong Chain.

See Claim.

See Chain.

A pattern that would be a Deadly Pattern if it weren't for the presence of extra candies called Heroes.

A Unique Rectangle is an Almost Deadly Pattern, and so is a BUG+n.

See the term Deadly Pattern.

Also see the page Deadly Patterns.

Synonym:  Unique Rectangle.

A four-Cell Flip-flop+n that would be a Deadly Rectangle if it weren't for the presence of extra candies called Heroes in some of its Cells.

There are applicable Tactics, often involving Chains.

See Unique Rectangle.

Flip-flop+n

An Almost Locked Set is a set of Cells in one House which would be a Locked Set if it weren't for the presence of some extra candie values in those Cells. If some move eliminates those extra candies, the set becomes an actual Locked Set.

The idea of an Almost Locked Set is specifically useful as a component of a Gotcha Chain or a Wrong Chain.

Abbreviation: ALS.

See Locked Set.

See Chain.

Almost Locked Set

An Attack Chain is a sequence of Cells via which you can prove that certain candies on the Grid get killed.

• Directed Attack Chain:  you pre-select specific candies which constitute a Worthy Target, and you construct a Chain to kill them (if possible).  Gotcha Chains and Wrong Chains are Directed Chains.

• Aimless Attack Chain:  you first find a type of Attack Chain based solely on its simple, recognizable form, and then you check to see whether there are any eligible candies to be killed in the Chain's Target Area. (See Chain for types of Aimless Chains.)

(The other kind of Chain is a Target Chain.)

See Chain.

(Scanning Tactic)

Block/Column-on-Row Shadowing:

Consider a Row that doesn't yet have a BigNum 9 entered. A 9 in any Block or Column that intersects that Row casts a Shadow on the Cell(s) in the intersection. If the Row has only one unshadowed empty Cell, that Cell must be where the 9 goes.

See B/C-on-R Shadowing.

(Scanning Tactic)

Block/Row-on-Column Shadowing:

Consider a Column that doesn't yet have a BigNum 9 entered. A 9 in any Block or Row that intersects that Column casts a Shadow on the Cell(s) in the intersection. If the Column has only one unshadowed empty Cell, that Cell must be where the 9 goes.

See B/R-on-C Shadowing.

(Bookkeeping Tactic)

Block-on-Column Claim:

The intersection of a Block and a Column is a 3-Cell Twit. If all the Block's 9-candies fall in that Twit, then any 9s in the Column outside that Twit can be killed.

See Claim.

(Bookkeeping Tactic)

Block-on-Row Claim:

The intersection of a Block and a Row is a 3-Cell Bandit. If all the Block's 9-candies fall in that Bandit, then any 9s in the Row outside that Bandit can be killed.

See Claim.

The Upper Band contains Rows 1,2,3.

The Middle Band contains Rows 4,5,6.

The Lower Band contains Rows 7,8,9.

See also the term Tower.

A Bandit is the horizontal three-Cell intersection of a Block and a Row.

There are three Bandits in a Block.

There are three Bandits in a Row.

See also the term Twit.

A digit (written large in a Cell) that is the number that the Cell will hold in the Solution.

A Big Number can be either a Clue (originally given when you got the Sudoku) or a digit that you've decided to place there as the final entry in the Cell.

Big Number

BUG

A Block is the 3-Cell by 3-Cell intersection of a Band and a Tower.

There are nine Blocks:

• the Upper Left, the Upper Center,
  & the Upper Right Blocks;

• the Middle Left, the Middle Center,
  & the Middle Right Blocks;

• the Lower Left, the Lower Center,
  & the Lower Right Blocks.

When a Block contains exactly two Cells that hold a 9-candie, those two 9s are called Block Twins.

The Strategy for solving a Sudoku by using Tactics that are made possible by the use of Candie Markup (pencil marks).

See Strategies & Tactics.

The Buddies of a Cell are all the other Cells in its Row, in its Column, and in its Block.

A Cell is said to see each of its Buddies.

Buddies are significant for two reasons:

• for an empty Cell "C", if any Buddy of C contains a BigNum 9, then C cannot accept a 9;

• for an empty Cell "C", if at some point you fill C with a 9, then you have to go through and kill the 9-candies in all of C's Buddies

(The same remarks apply to 8s, 7s, 6s,...)

A Deadly Pattern occupying all the empty Cells which would cause a puzzle to have no solution. The pattern consists of Pair Cells; the candies in these Cells (the deadly candies) satisfy certain restrictions.

A Sudoku never contains a BUG.

See Deadly Patterns.

(Bookkeeping Tactic)

A pattern occupying all the empty Cells which would be a BUG if it weren't for the presence of extra candies called Heroes in n of its Cells.

There are applicable Tactics, often involving Chains.

See BUG+n.

(Bookkeeping Tactic)

Column-on-Block Claim:

The intersection of a Block and a Column is a 3-Cell Twit. If all the Column's 9-candies fall in that Twit, then any 9s in the Block outside that Twit can be killed.

See Claim.

Column 4

Columns 4, 6, and 9

See candie.

A digit that an empty Cell will accept.

A list of currently acceptable candies is kept in every empty Cell (if you are using the Bookkeeping Strategy).

You kill some candies in some empty Cells every time you execute a Tactic.

You kill some candies in certain empty Cells every time a Crowning has taken place.

(The term candie is short for candidate.)

Keeping a list in every empty Cell of all the candies which that empty Cell will currently accept.

Executing a Tactic will kill some candies in some Cells.

When you enter a BigNum in a Cell, you then have to kill its Lookalikes in all the Cell's Buddies.

See Candie Markup.

The smallest unit of a Sudoku Grid. The 9 x 9 Grid has 81 Cells.

Each Cell will (finally) hold one BigNum.

A Chain can be one of two things:

• an attack mechanism (an Attack Chain);

• or an intended victim (a Target Chain).

See Attack Chain and Target Chain.

See Chain.

See

• B-on-R Claim
• B-on-C Claim
• R-on-B Claim
• C-on-B Claim

A Big Number in a Cell which is given as part of the original Sudoku.

A vertical sequence of 9 Cells.

The Columns of the Grid are numbered from 1 to 9 from left to right.

When a Column contains exactly two Cells that hold a 9-candie, those two 9s are called Column Twins.

A state of the Grid in which one of two things has occurred:

• there are two equal BigNums in some House;

• or there is a Cell that has no candies left.

A Conflict can arise in one of three ways:

• the puzzle is invalid;

• the player has made an error;

• or the player has deliberately made a wrong assumption in order to prove that the assumption is impossible.

For a Flip-flop+n or a BUG+n, if the assumed truth of every Hero (one by one) implies that one specific candie in one specific Cell gets killed, then you can kill that candie (because at least one of the Heroes must be true).

See Unique Rectangle and BUG+n.

Constituent Candies are the candies which define the structure of a Target.

Both of the candies in a Fault Point are its Constituent Candies.

A Fault Line is a Tightly Linked Twin Chain;  its Constituent Candies are all the Twins that define the Chain.

In an Almost Deadly Pattern, the Constituent Candies are the Heroes of the Pattern.

See Fault Point, Fault Line, and Tightly Linked Twin Chains.

See Almost Deadly Patterns; see the term Hero.

To crack a Sudoku means to find the Solution.

To crack a Fault Point (which is a specific kind of Pair Cell) means to kill one of its two candies.

To crack a Fault Line means to kill one of its Constituent Candies, which will activate the entire Fault Line. (A Fault Line is a Tightly Linked Twin Chain, and killing or crowning one of its defining Twins will determine the true/false status of all the Chain's defining Twins.)

The point of cracking a Fault Point or a Fault Line is that doing so is likely to crack the entire Sudoku, or at least to substantially weaken the Grid.

See Fault Point and Fault Line.

Compare the term exploit.

A candie in an empty Cell is crowned when you promote it to a BigNum — you have logically determined that, in fact, that Cell can accept only that candie.

If you crown a 9-candie in an empty Cell, you fill that Cell with a BigNum 9, and then you have to go through and kill all the 9-candies in that Cell's Buddies.

The candies that define a Deadly Pattern (a Flip-flop or a BUG).

An Almost Deadly Pattern (a Flip-flop+n or a BUG+n) is recognizable by the presence and distribution of the deadly candies; it is rescued by the presence of extra candies called Heroes.

See Deadly Patterns.

A pattern of Cells and candies in those Cells which would cause a puzzle to have no solution or to have multiple solutions.

A Sudoku never contains a Deadly Pattern.

See Deadly Patterns.

A four-Cell Flip-flop.

A Sudoku never contains a Deadly Rectangle.

See Flip-flop.

See Deadly Patterns.

A Locked Set is decomposable if it can be broken down into several smaller Locked Sets.

See Locked Set.

Twin-link Degree

A Sudoku that can't be solved by using Tactics that a human can carry out without having a heart attack. The Grid of a Diabolical Sudoku doesn't contain enough Pairs or enough Twins.

See Diabolical Sudokus and The Quest.

In a Sudoku, any one of the symbols 1 through 9.

A Directed Chain is an Attack Chain that you construct yourself to prove that some pre-selected candie is false.  You pre-select the candie to be killed on the basis that it is known to be a Worthy Target.

Gotcha Chains and Wrong Chains are Directed Chains.

(Opposite of Aimless Chain.)

See Gotcha Chain and Wrong Chain.

See Worthy Target.

See Chain.

A Cell that does not yet contain a Big Number.

If you are following the Bookkeeping Strategy, then you have put into every empty Cell the complete list of candies that the Cell will accept (and you update that list continually).

To exploit an Almost Deadly Pattern means to find a Troublemaker candie that would kill all the Heroes in the Pattern. Since that can't happen, the Troublemaker must be false. You will look for a Troublemaker whose demise would give rise to a bunch of useful moves, thus exploiting the existence of the Almost Deadly Pattern.

(Generally speaking, exploiting an Almost Deadly Pattern will not crack the Pattern, although in certain cases, namely a 1-corner UR, a Flip-flop+1, or a BUG+n, the Pattern will in fact usually get cracked (filled in with Big Numbers).

See Unique Rectangle and BUG+n.

Compare the term crack.

Synonym of see.

A candie in a Cell is false if that candie does not equal the BigNum that will appear in that Cell in the Solution.

A Fault Line is a long Tightly Linked Twin Chain whose defining Twins are sufficiently vulnerable to attack. It's a line of weakness in the Grid.

A Fault Line is a Worthy Target for an Attack Chain.

See Tightly Linked Twin Chains.

See Worthy Target.

See Chain.

A Fault Point is a Pair Cell with a high Twin-link Total (usually 5 or 6).  It's a weak point in the Grid.

A Fault Point is a Worthy Target for an Attack Chain.  It's also possible to launch a Smart Fork from a Fault Point.

See Twin-link Total.

See Worthy Target.

See Chain and Smart Fork.

To fill an empty Cell means to enter a BigNum in the Cell (changing it to a filled Cell).

A Cell that contains a Big Number (the digit that will be in that Cell in the Solution).

See 2-Fish and 3-Fish.

See 2-Fish and Other Fish.

A Deadly Pattern which would multiply the number of solutions to a puzzle by 2. The pattern consists of Pair Cells; the candies in these Cells (the deadly candies) satisfy certain restrictions.

A Sudoku never contains a Flip-flop.

See Deadly Patterns.

A pattern that would be a Flip-flop if it weren't for the presence of extra candies called Heroes in n of its Cells.

See Unique Rectangle, 6-Cell Flip-flop+n.

See Unique Rectangle.

Crowning one member of a Pair to see what happens, and then crowning the other to see what happens.

This does not have to be done haphazardly. See Smart Fork.

See the term move-connected.

(Bookkeeping Tactic)

This is an Attack Chain.

A Gotcha Chain is a double-headed Directed Chain whose two heads both face a target Cell containing a candie you want to kill. If one head of the Chain doesn't kill the candie, then the other one will.

See Chain.

The 9 x 9 matrix of Cells making up a Sudoku.

A group of Bookkeeping Tactics.

A Grid Sweep Tactic is usually applied by sweeping down the Grid and then across the Grid. Grid Sweep Tactics are all Fish Tactics.

See 2-Fish, 3-Fish, Sashimi, Splatterfoot.

A candie whose presence in a Cell prevents some pattern on the Grid from being a Deadly Pattern.

See Almost Deadly Pattern.

See Deadly Patterns.

(Bookkeeping Tactic)

In one House, if there are only two Cells that contain 8s or 9s, then those two Cells are a Hidden Locked Pair, and you can kill the non-(8,9) candies in those two Cells.

(Bookkeeping Tactic)

A set of N Cells in one House which are the only Cells in that House that contain a specific set of N candies.

See Hidden Locked Single, Hidden Locked Pair, Hidden Locked Trio.

See Hidden Locked Set.

(Bookkeeping Tactic)

In one House, if there is only one Cell that contains a 9, then that Cell is a Hidden Locked Single, and you crown its 9 (the other candies in the Cell are irrelevant).

(The term Hidden Locked Single is used to refer either to the Cell or to the 9 itself.)

(Same for 8s, 7s, . . .)

See Locked Single & Hidden Locked Single.

When a House contains several 9-candies, if all but one of them is killed, then the surviving 9-candie can be crowned, because it has become a Hidden Locked Single.

See Locked Single & Hidden Locked Single.

See Chain.

(Bookkeeping Tactic)

In one House, if there are only three Cells that contain 7s or 8s or 9s, then those three Cells are a Hidden Locked Trio, and you can kill the non-(7,8,9) candies in those three Cells.

This pattern is rarely used because it's very hard to spot.

See Hidden Locked Set.

A Row, a Column, or a Block.

The group of Cells shared by two different Houses:

• a Row and a Column intersect in a Cell;

• a Row and a Block either don't intersect, or they intersect in a Bandit;

• a Column and a Block either don't intersect, or they intersect in a Twit.

You kill (cross out) a candie in an empty Cell when you logically determine that, in fact, that Cell cannot accept that candie.

Target Area

(Bookkeeping Tactic)

This is an Attack Chain.

A Little ALS Chain is an Aimless Chain consisting of a two-Cell Almost Locked Set plus an exterior trigger Cell. This Chain will kill a specific candie-value in the Cells in its Target Area (if the candie-value occurs).

See Chain.

A group of Bookkeeping Tactics.

A Local Tactic applies to just one House or to a combination of two specific Houses.

See Locked Single, Locked Set, Hidden Locked Single, Hidden Locked Set, Claim.

(Bookkeeping Tactic)

This is not a Pair. It is a set of two Cells in one House which contain identical Pairs. The two candies making up the Pair can be killed in the other Cells of the House.

See Locked Set

(Bookkeeping Tactic)

This is not a Quartet. It is a set of 4 Cells in one House whose candies (taken together) involve only 4 digits a, b, c, d. The digits a, b, c, d can be killed in the other Cells of the House.

See Locked Set.

(Bookkeeping Tactic)

This is not a Quintet. It is a set of 5 Cells in one House whose candies (taken together) involve only 5 digits a, b, c, d, e. The digits a, b, c, d, e can be killed in the other Cells of the House.

See Locked Set.

(Bookkeeping Tactic)

N empty Cells of one House which contain only candies chosen from a specific set of N different candies.

See Locked Pair, Locked Trio, Locked Quartet, Locked Quintet.

(And see the degenerate case — Locked Single.)

See Locked Set.

(Bookkeeping Tactic)

A Cell that contains only one candie (as a result of recent Kills). You crown this candie.

(The term Locked Single is used to refer either to the Cell or to the candie itself.)

See Locked Single & Hidden Locked Single.

(Bookkeeping Tactic)

This is not a Trio. It is a set of 3 Cells in one House whose candies (taken together) involve only 3 digits a, b, c. The digits a, b, c can be killed in the other Cells of the House.

See Locked Set.

Lookalikes are all the instances of one specific candie-value which occur in different Cells of one House.

Lookalikes are Twins, Triplets, Quadruplets, Quintuplets, Sextuplets, Septuplets, Octuplets, or Nonuplets.

If a House contains exactly two Cells that hold a 9-candie, those 9s are Twins.

If a House contains exactly three Cells that hold a 9-candie, those 9s are Triplets.

If a House contains exactly four Cells that hold a 9-candie, those 9s are Quadruplets.

Two Twin Chains are loosely linked if they intersect at one or more Cells, but none of those Cells is a Pair Cell.

Loosely Linked Twin Chains are of no interest in themselves, but if the extra candies in a link Cell connecting two Twin Chains can be killed (by Wrong Chains) to the point that the link Cell becomes a Pair Cell connecting the two Twin Chains, then the Chains become Tightly Linked Twin Chains, which are then a Worthy Target for an Attack Chain.

See Twin Chain and Tightly Linked Twin Chains.

Put Candie Markup in [a Cell].

See the term Candie Markup.

(Bookkeeping Tactic)

A Unique Rectangle for which no Troublemaker Chains can be found but for which a Twin-based argument yields a very minor Kill.

See Unique Rectangle.

(This definition is here solely because the term move-connected is used in three entries of this table. It's not a term you need to worry about.)

A specific group of empty Cells on the Grid is move-connected if for any two Cells A and B in the group there exists a specific candie in A that you can assume true or false, and there then exists a sequence of Local-Tactic moves through group Cells only which leads to Cell B and kills or crowns one of B's candies.

If that's true regardless of whether you assume the initial candie true or you assume it false, then the group is fully move-connected.

(This definition could be made even hairier by allowing for the possibility that the initial or final "Cell" A or B is really a group of Cells constituting an Almost Locked Set or an Almost Claim. I don't think you want to suffer through all that.)

A Twin Chain is fully move-connected. Tightly Linked Twin Chains are fully move-connected. A Gotcha Chain is move-connected, but not fully move-connected. (The first two of these are Target Chains, and the last is an Attack Chain. They're not the same kind of thing and they don't have the same properties.)

A 2-, 3-, or 4-corner UR.

Synonym of Locked Set (to emphasize the contrast with a Hidden Locked Set).

(Scanning Tactic)

When eight of the Cells of a House have been filled in, it's obvious what digit goes in the remaining Cell.

See Nearly Full House.

A group of Bookkeeping Tactics.

A Network Tactic involves repeatedly jumping from one Cell to one or more of its Buddy Cells. Network Tactics are nonlocal:  they can affect Cells all over the Grid as they progress.

See Twin Tagging.

See Chain, Smart Fork.

A Locked Set is nondecomposable if it cannot be broken down into smaller Locked Sets.

See Locked Set.

For two identical candies in a Block:

Two 9-candies are oblique if they lie neither in the same Bandit nor in the same Twit.

(The opposite of oblique is aligned.)

See Claim and Twin Tagging.

oblique

(Scanning Tactic)

For any empty Cell, if you check all the Cell's Buddies and find that the Cell can accept only a 9, then you can enter a BigNum 9 in that Cell.

(This is a slow Tactic.)

When one Cell contains exactly two (different) candies, those candies are said to be a Pair.

A Cell that contains exactly two candies.

Candie Markup

When You promote a candie in an empty Cell, you enter that candie-value as the Big Number in the Cell.

When one House contains exactly four Cells that hold a 9-candie, those four 9s are said to be Quadruplets (same for 8s, 7s, 6s,...).

When one Cell contains exactly four (different) candies, those candies are said to be a Quartet.

When one Cell contains exactly five (different) candies, those candies are said to be a Quintet.

When one House contains exactly five Cells that hold a 9-candie, those five 9s are said to be Quintuplets (same for 8s, 7s, 6s,...).

(Scanning Tactic)

Row/Column-on-Block Shadowing:

Consider a Block that doesn't yet have a BigNum 9 entered. A 9 in any Row or Column that intersects that Block casts a Shadow on the Cells in the intersection. If the Block has only one unshadowed empty Cell, that Cell must be where the 9 goes.

See R/C-on-B Shadowing.

(Bookkeeping Tactic)

Row-on-Block Claim:

The intersection of a Block and a Row is a 3-Cell Bandit. If all the Row's 9-candies fall in that Bandit, then any 9s in the Block outside that Bandit can be killed.

See Claim.

Row 2

Rows 2, 5, and 7

The Cell at Row 3, Column 8

The four Cells at R4C1, R4C9, R6C1, R6C9

Usually a Wrong Chain produces a direct Conflict with the candie assumed true in the first Cell of the Chain. But when a Conflict is found out in the middle of nowhere while you're trying to construct the Chain, that's a remote Conflict.

See Chain.

A horizontal sequence of 9 Cells.

The Rows of the Grid are numbered from 1 to 9 from top to bottom.

When a Row contains exactly two Cells that hold a 9-candie, those two 9s are called Row Twins.

(Bookkeeping Tactic)

This is an Attack Chain.

A Same-Pair Chain is an Aimless Chain consisting of an even number of identical Pair Cells. If the constituent Pair is {8 9}, then this {8 9}-Chain will kill all the 8s and 9s in its Target Area.

See Chain.

(Bookkeeping Tactic)

Row-Based Sashimi in 9:

• Two Rows have Twin 9s.

• Two of the Row 9s are framed in one Column.

• The other two Row 9s lie in two different Columns of one Tower; any 9-candie facing these two 9s gets killed.

(Similar remarks for a Column-Based Sashimi.)

See 2-Fish.

The Strategy for solving a Sudoku by using Tactics that do not depend on Candie Markup (pencil marks).

See Strategies & Tactics.

A Cell is said to see each of its Buddies.

Also, a candie or a BigNum in a Cell is said to see any candie or BigNum in any of its Cell's Buddies.

Synonym:  face.

A Set is a group of (different) candies in one Cell.

A Set is a Pair, a Trio, a Quartet, a Quintet, a Sextet, a Septet, an Octet, or a Nonet.

If a Cell contains exactly two candies, those candies are a Pair.

If a Cell contains exactly three candies, those candies are a Trio.

If a Cell contains exactly four candies, those candies are a Quartet.

See

• R/C-on-B Shadowing
• B/C-on-R Shadowing
• B/R-on-C Shadowing

Silver Bullet Tactics are, by definition, the Tactics necessary for solving a Diabolical Sudoku. Whether such Tactics as they currently exist are really workable for a human Sudoku player is a matter of dispute.

See Diabolical Sudokus and The Quest.

(Bookkeeping Tactic)

If you have absolutely run out of moves, you can try a Smart Fork if a good Fault Point exists.

You scan the Grid to find a high-quality Fault Point (a Pair Cell with a high Twin-link Total), from which you will launch a Fork. Each of the Fault Point's two candies is assumed true in turn, and in each case you then make all available non-Chain moves.

A Fault Point of Twin-link Degree (3,3) or (2,3) will usually yield a Solution on one branch of the Fork and explicit Conflicts on the other branch.

See Twin Tagging and Smart Fork.

The state of a Grid where every Cell of the Grid is filled with a BigNum and there are no Conflicts.

A Sudoku is always constructed in such a way that it has one single Solution.

A Splatter of 9s is two or three 9-candies in one Bandit or in one Twit.

(Bookkeeping Tactic)

Row-Based Splatterfoot in 9:

• One Row has Twin 9s, a left one & a right one.

• Another Row has a 9 on the left and a Splatter of 9s on the right.

• The left Row 9s are framed in one Column.

• The right Row 9 and the 9-Splatter lie in one Tower; any 9-candie in the two Cells which face this 9 and the 9-Splatter gets killed.

(Similar remarks for a Column-Based Splatterfoot.)

See Splatter.

See 2-Fish.

If a Chain from a Fork leads neither to a Solution nor to a Conflict, it is said to have produced a Stalemate. You cannot conclude anything from a Stalemate.

See Smart Fork.

A Strategy consists of a (possibly large) group of Tactics.

The two Strategies for solving a Sudoku are Scanning and Bookkeeping.

See Strategies & Tactics.

A 9 x 9 Grid subdivided into nine 3 x 3 Blocks, where there are initial Clues in some of the Cells.  A Sudoku is constructed to have one single Solution in which every House will contain the Big Numbers 1 to 9.

Grid

When a House contains Twin 9s, if one of them is killed then the other can be crowned (because it becomes a Hidden Locked Single). This is a Surviving-Twin Crowning.

A specific procedure that results in killing or crowning a candie in some specific Cell or Cells.

See Strategies & Tactics.

Put Twin Tagging on [a candie].

See the term Twin Tagging.

The group of Cells in which some concrete Tactic will kill some specific candie-value (if that candie-value occurs).

On this site, Target Area is used in the discussion of Fish, Sashimis, Splatterfoots, and Aimless Chains.

A Target Chain is not an attack mechanism:  it is a sequence of Cells that is a Target, where killing one of the Chain's Constituent Candies would give rise to Kills or Crownings in all the Cells in the Chain. (You construct a separate Attack Chain to crack the Target Chain.)

A Tightly Linked Twin Chain is a Target Chain.

(The other kind of Chain is an Attack Chain.)

See Chain.

These Chains together constitute a Target Chain (it is not an attack mechanism).

Tightly Linked Twin Chains are a group of Twin Chains where the entire group is fully move-connected (because of Pair-Cell links between the Chains).

There are Tactics for attacking Tightly Linked Twin Chains.

(It is frequently convenient to use the singular, Tightly Linked Twin Chain, to refer to a group of Tightly Linked Twin Chains taken all together as one long Chain.)

See Twin Chain.

See Chain.

The Left Tower contains Columns 1,2,3.

The Center Tower contains Columns 4,5,6.

The Right Tower contains Columns 7,8,9.

See also the term Band.

When one Cell contains exactly three (different) candies, those candies are said to be a Trio.

When one House contains exactly three Cells that hold a 9-candie, those three 9s are said to be Triplets (same for 8s, 7s, 6s,...).

For a Flip-flop+n or a BUG+n, if the assumed truth of some specific candie (the Troublemaker) in some Cell implies that all the Heroes get killed, then you can kill the Troublemaker (because at least one of the Heroes must be true).

See Unique Rectangle and BUG+n.

A candie in a Cell is true if that candie equals the BigNum that will appear in that Cell in the Solution.

Synonym of Twit.

This is a Target Chain (it is not an attack mechanism).

A Twin Chain in 9 is a group of empty Cells where

• any two group Cells facing each other contain mutual Twin 9s;

• the entire group is fully move-connected.

There exist Tactics for attacking a Twin Chain.

See Chain.

• The Twin-link degree of a candie in a Cell is the number of Twins the candie has (in its Row, Column, and Block). This can equal 0, 1, 2, or 3.

• The Twin-link degree of a Cell is a tuplet specifying the Twin-link Degree of each candie in the Cell.  For the Pair Cell { 6  O8 } the Twin-link Degree is (2,3).

• (If your browser is Microsoft IE6, then click View / Refresh, because Microsoft randomly leaves off the underlines on the 6 and the 8 in the preceding paragraph, particularly when you use the upper or lower scroll buttons or the mouse scroll-wheel.)

See Twin Tagging.

The Twin-link Total of a Cell is the sum of the Twin-link Degrees of all its candies. For a Pair Cell of Twin-link Degree (2,3) the Twin-link Total is 5.

See Twin-link Degree.

See Twin Tagging.

If a House contains Twin 9s, then the two Cells that hold those 9s are said to be Twin-linked. (Same for 8s, 7s, 6s,...)

When one House contains exactly two Cells that hold a 9-candie, those two 9s are said to be Twins (same for 8s, 7s, 6s,...).

• Twin 3s in a Row are tagged like this: 3

• Twin 5s in a Column are tagged like this: 5

• Obliquely located Twin 6s in a Block are tagged like this: O6

Twin Tagging makes Twins and the relations between them visible. It is useful for finding Fault Points and for finding and clearly delineating a Fault Line.  (Fault Points and Fault Lines are Worthy Targets for an Attack Chain:  cracking such a Target can crack the Sudoku or at least clean up the Grid substantially.)

See Twin Tagging and Chain.

A Twit is the vertical three-Cell intersection of a Block and a Column.

There are three Twits in a Block.

There are three Twits in a Column.

Also called Turret.

See also the term Bandit.

A Sudoku is always constructed to have a unique Solution, which means that it has one and only one solution.

(Bookkeeping Tactic)

A Unique Rectangle is an Almost Deadly Rectangle. It is a four-Cell Flip-flop+n that would be a Deadly Rectangle if it weren't for the presence of extra candies called Heroes in some of its Cells.

There are applicable Tactics, often involving Chains.

See Unique Rectangle.

A group of Bookkeeping Tactics.

Uniqueness Tactics involve looking for the occurrence of a specific Almost Deadly Pattern. They are based on a unique-solution argument.

See Deadly Pattern.

See Unique Rectangle and BUG+n.

When you fill an empty Cell with a BigNum 9, then you have to update the Grid by killing all the 9-candies in that Cell's Buddies. (Same for 8s, 7s, 6s,...)

Unique Rectangle

The whole idea of a Worthy Target is that you would prefer not just to look for an Aimless Chain that might kill something somewhere. Rather, you would like (1) to find a really good Target whose demise would produce a major clean-out of the Grid and (2) to construct a Chain to attack that Target.

Worthy Target usually refers to a Cell or a Chain of Cells where killing a Constituent Candie of the Target is likely to crack the entire Sudoku or at least to substantially weaken the Grid.  (An individual candie whose demise would noticeably weaken the Grid is also a Worthy Target.)

A Fault Point or a Fault Line are Worthy Targets.  A candie whose eradication would cause two loosely linked Twin Chains to become tightly linked is a Worthy Target.

The Heroes of an Almost Deadly Pattern are a temporary Worthy Target: if you can find a Troublemaker candie from which you can launch Chains that would kill all the Heroes in the Almost Deadly Pattern, then you know that that Troublemaker can't be true.

See Fault Point, Fault Line, and Tightly Linked Twin Chains.

See Almost Deadly Pattern, and Troublemaker approach.

See Constituent Candie.

See Chain.

See Unique Rectangle and BUG+n.

(Bookkeeping Tactic)

This is an Attack Chain.

A Wrong Chain is a Directed Chain whose first Cell contains a candie that you're trying to prove false (via the fact that the Chain produces a Conflict when the candie is assumed true).

See Chain.