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If r7c3 <> 8, then r6c6 = 8: If r6c6 <> 8, then r7c3 = 8. So r7c6 <> 8.

How to describe this in Eureka, remembering that in an XY Chain the strong links are within bi-value cells and the links between the cells are all weak links, or acting as weak links? How about:

(8=7)r7c3 – (7=3)r5c3 – (3=7)r6c2 – (7=6)r6c7 – (6=8)r6c6 => -8r7c6

A simple elimination which doesn’t immediately solve the puzzle, but the next one does:

(1=2)r5c4 – (2=7)r5c8 – (7=6)r6c7 – (6=8)r6c6 – (8=1)r6c1 => -1r5c1, r6c4

Any thoughts on the notation?