# Advanced Techniques of Sudoku Solving

## Closed candidate

Sometimes, number is valid only for grid cells from one row (or one column) of the region, meanwhile one of these cells will necessarily contain the value of this number. Consequently it is invalid for all grid cells of the same row (or column) but for other region. You can eliminate such candidates from the list of valid values of grid cells described before.

## Naked Pair

A naked pair is two identical candidates in a particular row, column, or region. If you find a naked pair, you can remove such candidates from all other cells in the row, column or region, where the pair is located.

## Naked Triplet

If three cells in a group (line, column or region) have identical three valid numbers and nothing more, other cells of this group cannot hold the values of these three. Such cells are named "naked triplet". Also, it is possible that some cells from the triplet contain only two values from the three values. You can remove triplet values from all other cells in the row, column or block where the triplet is located.

## Naked quad

If four cells in a group (line, column or region) have identical four valid numbers and nothing more, other cells of this group cannot hold the values of these four. Such cells are named "naked quad". It is possible that some cells from the quad contain only two or three values from the four values. You can remove quad values from all other cells in the row, column or block where the quad is located.