The New Sudoku Players' Forum

[Cec]

".. Is there a piece of logic that dictates that r8 has to be the base of the x-wing and r7 cannot be?.."

Ralph & Cynthia,
To complement the above help you might also like to look at this Thread and particularly the following criteria for X-wing formation and exclusions.

" ..Remember that the "X-wing" technique requires the particular candidate to appear twice and only twice either in two rows and sharing the same two columns in which case the eventual exclusions occur in columns or, using the same logic, where the particular candidate appears twice and only twice in two columns and sharing the same two rows then the exclusions occur in rows..."

Cec

[Guest]

A. Okay, we see that now.
B. When I asked, "Why not r7c69?", I was back looking at my original partial solution, so I still had 3 1s in r8 too, so it looked like the same situation. Thanks all for your help. We have a much better understanding of the x-wing technique now. Ralph & Cynthia