... by: Roman
The Nice Rule 2 examples have 2 terminating weak links.Is this correct?
Andrew Stuart writes:
Nope. Wrong examples. Fixed






Grouped XCycles Chaining strategies such as XCycles use links that connect cells on the board. It is possible to expand on the idea of a "cell" to something a bit larger, namely a "group" of cells. I prefer the word "node"  which in 90% of cases will be a single cell  but can be two or three cells in the same unit. You might wonder how we can use more than one cell and think of it as a node between two links, but there is some cool logic here. We must go all the way back to Pointing Pairs and Pointing Triples. They attack cells along the row or column on which they are aligned. They also must be in the same box to be a coherent unit. Our “grouped” cells are just Pointing Pairs/Triples and we’re going to use them as part of a chain or Nice Loop.
At the point it's also worth recapping something about Continuous Alternating Inference Chains. Firstly, its doesn't matter which way you walk round the loop  clockwise or anticlockwise, secondly, it doesn't matter which cell you start with and thirdly, each cell could be ON or OFF  as long as you alternate. Even with the convention of starting with the top leftmost cell, there are four ways we could write down the chain:
I've deliberately used neutral colours in the diagram above (yellow and blue) not to given the impression there only one way to write the same chain. However, the solver will return very positive red and green highlighting but that's because it has discovered one of those four ways first and discarded the other three identical ways.

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