Methods:

Candidate Reduction

Locked Candidate

Hidden Candidates

Naked Candidates

X-wing, Swordfish, Jellyfish

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Sudoku Instructions - Methods To Remove Candidate Numbers

Candidate Reduction Methods - Examples

The program can remove or eliminate candidate numbers with these so-called reduction methods: locked candidates, hidden matched candidates (pairs, triples, quads); naked matched candidates (pairs, triples, quads), x-wing, swordfish, jellyfish.

Do not worry! The Sudoku Solutions Program will explain to you in easy and simple terms how these methods with rather strange names actually work!

In using these methods, the program will show you the identified candidate numbers in blue. At the same time the program will show you the candidate numbers, which can be removed, in red as you can see in the examples below.

Thus the program will help you finding candidate numbers, which can safely be removed.

Locked candidate:

In row 3 candidate number 3 is present only inside block L. So in that block number 3 is locked in row 3 since it can only be in that row (blue numbers).

Thus you can remove 3 as a candidate in the other rows inside block L, that is in the red squares in row 1.

Using the program you can do this simply by clicking on 'Perform This Reduction'.

Hidden candidates (pair):

In block J candidate numbers 1 and 5 form a matched pair (blue numbers) 'hidden' among other candidates (here 8) in squares A1 and B1. Candidate numbers 1 and 5 are not present in any other square in the block. Therefore they must be in those two squares.

Thus you can remove other candidates (here 8 - shown in red) from the squares.

Using the program you can do that simply by clicking on 'Perform This Reduction'.

Hidden matched candidates with triples or quads can be identified in a similar way.

These more difficult reduction methods are explained in the program.

Download The Sudoku Instructions Program Now.

Naked candidates (pair):

In row 1 candidate numbers 1 and 5 form a naked matched pair (blue numbers) in squares A1 and B1. They are called 'naked' because they are alone in two squares. These numbers must therefore be in those two squares (A1 and B1).

Thus you can remove candidate 5 from the red square.

Using the program you can do that by clicking on 'Perform This Reduction'.

Naked matched candidates in triples or quads can be identified in a similar way.

These more difficult reduction methods are explained in the program.

X-wing, Swordfish, Jellyfish:

Candidate number 1 forms an X-wing in the blue squares because in rows 6 and 8 candidate number 1 is only present in columns D and F. So, in these columns candidate number 1 must be in rows 6 and 8.

Therefore in these columns you can remove candidate number 1 (shown in red) from the other rows.

Using the program you can do that by clicking on 'Perform This Reduction'.

Swordfish (one candidate number in just 3 rows or columns) and Jellyfish (one candidate number in just 4 rows or columns) can be identified in a similar way.

These very difficult reduction methods are explained in the program.

Download The Sudoku Instructions Program here.