Eliminating

Removing a candidate from the grid.

An empty Sudoku grid starts with 729 candidates. Several of them are removed because a given is present in the cell. Each given automatically eliminates the 8 remaining candidates from that cell.

Further eliminations can be made by examining the houses. A house which already contains a certain digit does not allow another placement. The remaining candidates for that digit can therefore be eliminated from the house. These are also known as direct eliminations.

When singles are placed, more direct eliminations can be made.

Finally, the player must use more advanced solving techniques to make additional eliminations. These are indirect eliminations, because they are not the immediate result of an individual placement.