Tredoku is a logic-based number placement puzzle in 3D space. The objective is to fill a spatial grid much like classic sudoku so that each column, each row and each of the 3×3 boxes (also called blocks or regions) contains the digits from 1 to 9 only, i.e. once each.

Unlike classic sudoku, the Tredoku game's open and changing spatial grid allows many more game design options while retaining the original game rules.

At the beginning of the game the puzzle setter provides a partially completed grid for the player to complete following the rules.

The flat grid-bound classic sudoku puzzle was invented by an American architect, Howard Garnes, in 1979 and published by Dell Magazines under the name "Number Place". It became popular in Japan in 1986, after it was published by Nikoli and given the name Sudoku, meaning single number. The Tredoku puzzle was invented by a young architect for Mindome Ltd. in 2006 and was first introduced in fall 2008.

There are a few distinctive differences between Tredoku and classic sudoku:
*Tredoku uses an open spatial grid system that could be infinitely expanded, retaining the original sudoku rules, while classic sudoku uses a closed 3x3 square grid (also used in classic sudoku variations)
*Tredoku is designed in simulated three dimensional space using a simple technique of shading and skewing, while classic sudoku uses a flat grid surface
*Tredoku, because it is in 3D, permits rows and columns to be straight, tilted or bent at a 90 degrees angle to the remainder of that row or column.
*Tredoku uses right/left brain power simultaneously - both spatial perception and logic in synergy, while classic sudoku uses left brain logic only
*Tredoku has an infinite number of game forms, while classic sudoku has the basic square 3x3 grid form, and some variations based on the flat grid design

The name Tredoku is a hybrid word built from the prefix "tre-" meaning "three" in Italian and the suffix "-doku" derives from the original flat game's name. The name is a worldwide trademark of game publisher Mindome Ltd.

The strategy for solving a Tredoku puzzle may be regarded as comprising a combination of three processes: scanning, marking up, and analyzing, just like classic sudoku.

While scanning in Tredoku is quite similar to classic sudoku, it uses spatial perception making scanning a bit more challenging perceptually but not logically.
Scanning is performed at the outset and throughout the solution. Scanning consists of two techniques:
*Cross-hatching: The scanning of straight or tilted and bent rows to identify, by a process of elimination, which line in a region may contain a certain numeral. The process is repeated with the straight, bent or tilted columns. It is important to perform this process systematically, checking all of the digits 1-9. By scanning you can look for pairs within three rows or three columns of a box set to decide the possible positioning of the 3rd member of that number-pair. You then mark-up the possible places for that 3rd number.
*Counting: The counting of the numbers 1-9 in boxes, straight tilted or bent rows and straight, tilted or bent columns to identify missing numerals. Counting based upon the last numeral discovered may speed up the search. It also can be the case, particularly in tougher puzzles, that the best way to ascertain the value of a cell is to count in reverse—that is, by scanning the cell's region, row, and column for values it cannot be, in order to see what remains. By doing this it may be possible to reduce a cell's options to a single entry, or a pair of possible entry for later elimination as the puzzle is filled further.
Advanced solvers look for "contingencies" while scanning, narrowing a numeral's location within a row, column, or region to two or three cells. When those cells lie within the same row and region, they can be used for elimination during cross-hatching and counting.

Subscript notation
In subscript notation, the candidate numerals are written in subscript in the cells. Using two colors, or mixing pencil and pen marks can be helpful.

Difficulty levels
Difficulty level in Tredoku is based on three factors:
*Number of shapes in each game - game designs vary from 7 shape-games to infinite
*Number of clues - same as in classic sudoku
*The shape of the game - more flat parts make it easier to solve, while bent designs make it more visually challenging

Beginner's level is intended for those who are not familiar with classic sudoku rules and would like to begin with Tredoku. The puzzles are limited in size.

Easy level is intended for those who are already familiar with classic sudoku. The puzzles range from 9-14 blocks each.

Medium level is intended for those who are already familiar with Tredoku. The puzzles range from 15-20 blocks each.

Hard level is for true Tredoku masters. The puzzles range from 20-25 blocks each.

Monster puzzles are designed to take much longer but their difficulty level could be set at any of the above levels.

Tredoku Kids
Tredoku has introduced logic/spatial puzzles for ages 5-7 and 8-11. The Tredoku Kids website ( has guidance for parents and educators as well as sample games.

Age 5-7
These games use simple 2x2 blocks with colorful objects, short number or letter sequences. The games are built around the graded learning requirements in logic and math for kindergarten to second grade and develop basic spatial visualization skills.

Age 8-11
These games move from 2x2 through 2x3 to regular 3x3 blocks with number and letter sequences. These levels match the learning progress of these age groups and develop their spatial visualization skills.

Tredoku for Seniors
Use of puzzles such and mind games such as crossword and sudoku are known to be beneficial for keeping and even improving seniors' mental agility. Tredoku, with its added spatial feature, will further enhance seniors' puzzle solving experience while also improving their spatial cognition.

Tredoku books
The first released book in the Tredoku series of books is Tredoku easy - book 1 intended for those already familiar with classic sudoku. The second book intended for new players who have very little or no experience with classic sudoku rules, will be released around the middle of October, 2008 and will be called Tredoku beginners - book 1.
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