This post uses two grouped AIC ANL from Hodoku to illustrate how such chains are inspired and constructed. After the first, readers are challenged to try this approach on the following examples, with checkpoint to follow.
I was prepared to skip the next four Hodoku examples of grouped AIC chains, thinking that, beyond the addition of grouped chains, there would be nothing new in them. But of course I had to try one. That led to demonstrations that grouping expands the possibilities for AIC ANL, and suggestions on finding them.
So here we are with Hodoku’s first Grouped Nice Loop/AIC. We’re going to call them Grouped AIC 1, 2, 3 and 4. After looking at Grouped AIC 1, you might want to try some of the others, before reading my version.
As expected, line marking was a chore. That completed, I added the AIC hinges and set out to transcribe the Hodoku grouped AIC chain into Sysudoku chain graphics, for “the better to see you with, my dear ” (Wolf to Little Red Riding Hood).
Hodoku knows exactly what premise to start a successful grouped AIC , but let’s think seriously on how a human could find this confirming ANL.
For example, on the 2- panel, you might see the 2-group above as part of the 2-chain on the left. Frustrated at extending from 2 or 9 in r2c1, you switch the c1 link back to a slink, to use an r2 wink and look for the confirming ANL, as on the right. Moving to r2c5 to extend it, the North 8-group becomes a way to do that. It provides the wink and slink out.
That much done, the chain completes easily, giving the Hodoku loop.
But there is another way to complete it.
Continuing from the 8-group, you can use two more 8-groups and an AIC hinge to enter the 2-group, completing the confirming ANL. Or you can drop the 2-group and the confirmation slink and use the three 8-group ANL to eliminate two rival 2-candidates in the SW box to get the same result.
What would you think if you came up with this alternative, and Hodoku check pointed you with the solution it gives. I’d be sure I’d made a mistake.
Moving on, in Grouped AIC 2 sysudokies seeing the bizarre mass of candidates would probably invest in some coloring in the bv bands around it. This nets a trap 4r9c5, but more tellingly, the three link 1-chain in the blue/green cluster could prompt a search for an AIC connection.
The 2-panel helps with a grouped slink to escape from r9c9, and makes it easy to see the c4 grouped slink into r6c4. Grouped chains are usually found when the search is focused in this way. The entire example is below.
As to finding this AIC nice loop, the unlikely Hodoku premise that r9c9<>2 was undoubtedly made after the nice loop was found, not before.
Next time we continue looking for plausible reasons for constructing grouped AIC with Hodoku examples 3 and 4.
Want to get there first? It would be great to hear from you before the post comes out.