Samer,
I think the reason you didn't see any cells the x-wing in 9's could exclude is because the locked candidate 9's in box 6 (top row) make those same exclusions and you had already done that. I was trying to illustrate that, many times, there is more than one logical way to exclude the same candidates. It should be that every time one spots two or more ways to make the same exclusions it should be possible to 'bank' one to be able to use whenever one needs it, but I haven't been able to find that particular bank.
Tracy
