emm wrote:I find remote locked pairs the hardest concept of all the basic techniques to visualise. I guess it's probably the same principle but the explanation of it seems so much more complicated than either strong links, XYchains or colouring - which in this case immediately removes 5 candidate 2s.

emm,

I'm not positive that you were asking for this, but...

I've always thought finding remote locked pair deductions was very easy. Here is my method. First identify the bivalue cells with a particular pair of candidates {xy}. Start at any of them and say "same". Now travel to another which sees the first cell and say "different". Travel to another that sees the second and say "same". Travel to another that sees the third and say "different", and so on. Any time you get to a cell and say "different", then you can eliminate x and y from any cell which sees the initial cell and the current cell. Of course, there is no guarantee that you picked your initial cell correctly, but with practice it is easier to pick out the right starting point.

In Ruud's example, I would start at r4c2 and say "same". Then move to r4c8 and say "different", then to r5c7 and say "same" and then to r9c7 and say "different". Now any cell which sees both r4c2 and r9c7 cannot have a 2 or 3, hence the exclusion in r9c2.

I hope this helps, or if you already knew this, I hope I haven't insulted your intelligence.