Hidden quad strategy for solving sudoku
Advanced strategies
Hidden quad
We will use this technique when we have the four same candidates in four cells of the same block, line or column.
If in this area (block, line or column), the four candidates are present in only four cells, then the other candidates have to be removed.
Example
Even by knowing that a hidden quad is in this line, will you find it? The exercise is very difficult!
They are the 1, 3, 7 and 8.
The other candidates in these four boxes can be eliminated.
Strategies list
Elimination of candidates by interaction in the same area
Elimination of candidates by interaction in several areas
Elimination of candidates by interaction in all the puzzle
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