... by: David P BirdAndrew the strong links you should be focusing on are those in the four bi-value cells in each example. In example 2 we get a sequence: (2'=3")r1c9 – (3'=4")r9c9 – (4"=5')r8c7 – (5'=2")r2c7 – Loop. Here all the odd(') or all the even(") numbered candidates will be true. This kills other 3s in c3, 4s in b9, 5s in c7 and 2s in b3, so it isn't necessary for 3 & 5 to be bilocal in the columns. You are therefore looking for an X-wing pattern made up of four bivalues with each side having a linking digit.
Andrew Stuart writes:
Quite right. I might change the focus of the search and strong links as you suggest and see if I get any extra hits with this search. I suspect that may still not produce enough extra value to bring it back into the solver - it is currently 'depciated' and unused. These results ought to pop out of several of the AIC and chaining strategies, but I'll need to do some testing. In the job queue.