Sudoku Solving

Basic Techniques
Single In Box
When there is only one cell in the box which can contain a certain value, this value can be safely assigned to this cell. Read more...
Single in Row/Column
This technique is based on the fact that every row must contain every value once. Read more...
Moderate Techniques
The following techniques are more difficult to spot because they require that every candidate value is carefully written down. This is a very time-consuming and precise task. Fortunately, this task can be carried out by a computer program. This can spoil the fun of completing the more simple puzzles, but it can still be very challenging when solving more advanced ones.
Naked Single
After writing down all the candidate values into the cells, you can come across a Naked Single, which means that there is only one possible value for that cell. Read more...
Pointing Pair
When a specific candidate value inside a box is restricted to one row or column, you can use the Pointing Pair technique. This means that you can exclude the same candidate value from other boxes in the same row or column. Read more...
Box Line Reduction
When a specific candidate value in a row or column only occurs in one box, this value can be exluded from other cells in the same box. Read more...
Advanced Techniques
Advanced Techniques are based on the same principals as the other techniques. They are generally more difficult to spot. A new term which will be introduced here is the group. A group can be a row, column or box.
Naked Pair
If two cells in the same group contain exactly the same two candidate values, these candidate values can be excluded from other cells in the group. Read more...
Naked Triple
If three cells in the same group contain exactly the same three candidate values, these candidate values can be excluded from other cells in the group. Read more...
Naked Quad
If four cells in the same group contain exactly the same four candidate values, these candidate values can be excluded from other cells in the group. Read more...
Hidden Pair
If two cells in a group contain an identical pair of candidates and no other cells in that group contain those two candidates, then other candidates in those two cells can be excluded. Read more...
Hidden Triple
If three cells in a group contain an identical pair of candidates and no other cells in that group contain those three candidates, then other candidates in those three cells can be excluded. Read more...
Very Advanced Techniques
These Very Advanced Techniques require the player to use the whole puzzle, instead of just parts. Sometimes techniques are chained or multiple techniques can be used together to solve very challenging puzzles.
Remote Pair
When chaining multiple Naked Pairs, a Remote Pair can be used to remove candidate values. Read more...
X-Wing
This is another method of reducing the candidates when two rows have the same candidate only in the same two columns. Read more...
Sword-Fish
Generalisation of the X-Wing pattern. Read more...
XY-Wing
Generalisation of the X-Wing pattern. Read more...
XYZ-Wing
Generalisation of the XY-Wing pattern. Read more...
Empty Rectangles
The Empty Rectangles uses the same logic as the X-Wing technique te exclude candidate values. Read more...
Colors
When a group contains only 2 of the same candidates, at least one of these candidates must have this value. By coloring these pairs, candidates can be excluded. Read more...
MultiColors
Generalisation of the Colors technique. Read more...
Nice Loop
Use strong and weak links to exlude candidates or assign values. Read more...
Forcing Chain
Chain pairs to exlude candidates or assign values. Read more...
Bug
Use the information that the puzzle only has one solution to exclude candidate values. Read more...
Unique Rechtangles
Use the information that the puzzle only has one solution to exclude candidate values. Read more...
Guess
Some puzzles cannot be completed using logic steps only. Read more...