| Ariadne's thread = fancy name for trial and error. (See also bifurcation and guessing).
Bifurcation = a widespread name for trial and error, whose origin is unknown. (See also Ariadne's thread and guessing).
Box line reduction strategy =
a form of intersection removal in which candidates which must belong to a line can be ruled out as candidates in a block (or box) that intersects the line in question.
Candidate =
potential value for a cell.
Cells = groups of squares (neither rows nor columns) which are constrained by the one rule. An M×M grid contains M cells; each cell has M squares. If M is not a prime number, then a cell is a rectangle (or, if possible, a square). If M is a prime number then a cell is a polyomino.
Chain =
a sequence of contingencies connected by alternate values.
Clues = the numbers which are filled into the grid to begin with. These are not to be changed in the course of completing the puzzle. (See also independent clues).
Columns = the squares lined up one below the other. We count them from left to right. An M×M grid contains M columns; each column has M squares.
Contingency =
a condition limiting the location of a value.
Counting = the
process of stepping through the values for a row, column or block to see where they can or cannot be used
Cross hatching = the
process of elimination that checks rows and columns intersecting a block for a given value to limit the possible locations in the block.
Depth first enumeration = a systematic method for exploring all possibilties in a branching tree od decisions. In the context of Su Doku, whenever one has more than one possibility at a square, one explores each possibility one by one. This is closely related to "trial and error", but there one stops as soon as one reaches an acceptable possibility. In this case one enumerates all possiblities. (A fancy coinage for this is the garden of forking paths).
Garden of forking paths = a fancy name for depth-first enumeration.
Givens = another name for clues.
Go Doku = the name for the puzzle on a 5×5 grid. It is an example of a Sub Doku and a Prime Su Doku.
Grid = the setting of the puzzle. An M×M grid contains M2 squares to be filled in.
Guessing = an inaccurate term for trial and error. (See also Ariadne's thread and bifurcation).
Hidden Pair =
2 candidates that appear only in 2 cells in a row, column or block. Other candidates in those 2 cells can be eliminated.
Hidden Single =
a candidate that appears with others, but only once in a given row, column or box.
Higher circuits =
related locations outside the immediate row, column and grid. The locations are related by value contingencies.
Hints = another name for clues.
Independent clues = the set of clues in a puzzle which cannot be deduced from each other. Given one set of clues there may be more than one way to pare away some to leave only independent clues.
Intersection removal =
when any one number occurs twice or three times in just one unit (or scope) then we can remove that number from the intersection of another unit. For example, if a certain number must occur on a certain line, then occurrences of that number found in a block that intersects this line can be ruled out as candidates. Sometimes called Pointing (or matched) Pairs (or twins)/Triples (triplets) as they point out a candidate that can be removed.
Locked Candidate =
a candidate limited to a row or column within a block.
Maximum Su Doku = the class of puzzles which have the maximum number of independent clues needed to allow a complete and unique solution.
Minimum Su Doku = the class of puzzles which have the minimum number of clues needed to allow a complete and unique solution.
Naked Pair =
2 cells in a row, column or block, which together contain only the same 2 candidates. These candidates can be excluded from other cells in the same row, column or block.
N-fish =
analogues of hidden pairs/triples/quads/... A pattern formed by all candidate cells for some digit in N rows (or columns), that spans only N columns (rows). All other candidates for that digit in those columns (rows) can then be excluded. Names for various N-fish:
* 2-fish : x-wing
* 3-fish : swordfish
* 4-fish : jellyfish
* 5-fish : squirmbag - For 9×9 Sudoku, there's no in point naming higher-order (>4) fish, since every N-fish comes paired with a 9-N fish whose effect is the same (thus any 5-fish is paired with a jellyfish; any 6-fish with a swordfish; any 7-fish with an x-wing; any 8-fish with a hidden or naked single). Nevertheless, a 5-fish is occasionally called a squirmbag.
* 6+ fish : 6-gronk, 7-gronk.. - these patterns are only useful for Sudoku larger than 9×9.
Nishio =
what-if method of elimination, where the use of a candidate is eliminated, that would make its other (necessary) placements impossible.
One rule = the only rule of M×M Su Doku: "Fill in the grid with numbers from 1 to M such that each number occurs exactly once in each row, column and cell without changing the clues".
Remote Pairs =
When a long string of naked pairs that leads around the grid exists, any cells that are in the intersection of the cells at the beginning and the end of the string may not be either of the numbers in the naked pairs, for example, 4 and 7.
Roku Doku = the name for the puzzle on a 6×6 grid. It is an example of a Sub Doku.
Rows = the squares lined up side by side. We count them from the top down. An M×M grid contains M rows; each row has M squares.
Satisfactory puzzled = those which require no trial and error in solving.
Scanning =
the process of working through a puzzle to look for or eliminate values.
Shi Doku = the name for the puzzle on a 4×4 grid. It is an example of a Sub Doku.
Single or Singleton or Lone Number =
the only candidate in a cell.
Squares = the places which have to be filled in. An M×M grid contains M2 squares.
Su Doku = usually means the puzzle on a 9×9 grid. In these web pages it is the generic term embracing all Sub Dokus and Super Dokus.
Sub Doku = means the puzzle on an M×M grid where M<9. These include M=4, called Shi Doku, M=5, called Go Doku, and M=6, called Roku Doku.
Super Doku = means the puzzle on an M×M grid where M>9.
Swordfish =
see N-fish (with N=3).
The One Point Rule =
fill in all (blank) cells so that each row, column and box contains the values 1-9. Same as: fill in the grid so that each row, column and box contains the values 1-9 exactly once, without changing the clues.
Trial and error = a systematic method for finding the solution to a puzzle, involving assuming a value at one square, and proceeding until a contradiction is found, another assumption is needed, or the puzzle is solved. If a contradiction is found, then one goes back and changes the assumed value. Under the name depth-first search, it is known to computer science as a general technique for finding the solution of any problem which has finite (but possibly very large) number of outcomes. If done unsystematically, it resembles guessing. (Also called Ariadne's thread and bifurcation).
Trio =
3 cells in a unit sharing 3 numbers exclusively. See triples and quads.
Triples and quads =
the concepts applied to pairs can also be applied to triples and quads.
X-wing =
see N-fish (with N=2).
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