by **Karyobin** » Sun Oct 02, 2005 6:18 pm

The X-wing does help, and I'll explain why.

There is no Naked Triple {2,8,9} in Column 8. There is a Naked Quad {2,4,8,9}, but this only serves to identify the Hidden Pair {1,6} in that column. By identifting the Hidden Pair {1,5} in Box 7, you lock the 9's in Row 7 into that box. From this you can exclude the 9 as a candidate from r7c6 and r7c8, leaving the remaining two 9's having to be in r9c7 and r8c6.

Remember the X-wing? That allowed you to remove a candidate 2 from r1c7. Now, the 9 you just placed in r9c7 allows you to do the same with the candidate 9, leaving r1c7 to be 8.

The next step was to find candidate 8's locked in a row in Box 6, allowing you to remove a candidate 8 from r5c2, resulting in a Hidden Pair {2,4} in Column 2. See the 6?

The rest, as people round here have started saying, is trivial.