Hi guys, I'm making a sudoku solver which can only use techniques and not brute force/backtracking, I have a number of techniques implemented in my program but I'm kind of stuck on what technique to use next.

I have a sample of 10 random hard puzzles and at the moment I'm completely solving 6 of them could someone have a look at my partially completed puzzle (possible candidates included) and maybe show me the next technique to code.

puzzle is http://i43.tinypic.com/zugnlh.png

This would be a great help thanks.