Sudoku: Nishio solving technique

Nishio

This is a limited form of trial and error. For each candidate for a cell, it asks the question:

If I put this number in this cell, will this prevent me from completing the other placements of this number?

If the answer if yes, then that candidate can be eliminated.

 

Here are some Sudoku puzzles that can be solved using the Nishio technique: (What are these?)

nishio1.sdk	nishio2.sdk
nishio3.sdk	nishio4.sdk

 

(My thanks to "rubylips" for providing the sample puzzles.)