
Claiming 

If the only instances of a candidate within a row or column are in the same box, you can eliminate candidates of that value from any other cell in the box. Consider the above example. In the fourth column from the left the only two 4's are in the same box (center). Thus the candidate 4 can be eliminated from the other cells in that box.
Because the result of this technique is only the elimination of a candidate, it requires either all the candidates to be filled in or the direct result of a hidden single to be spotted. Sudoku Snake gives it a skill value of 20.






