Nice Loops
Chains that close into a loop. A fully alternating loop forces eliminations along every weak link around it, often several at once.
Candidate 6 traces a closed loop through four cells, alternating strong and weak links all the way around.
How to spot it
- 1Construct an alternating chain that returns to its start.
- 2A closed alternating loop means every weak link is off.
- 3Eliminate the candidate along each weak link.
When to use
On the hardest grids, where a single loop cascades many eliminations.
When not to
If a short chain suffices, skip the loop — they're demanding to trace.
Common mistake
Accepting a loop that isn't perfectly alternating, which yields false eliminations.
Worked Example
A nice loop is a chain that closes back on itself, returning to its starting cell after an unbroken sequence of alternating strong and weak links. Because the loop is fully alternating all the way around, every single weak link in it turns out to force an elimination — not just the two original endpoints, the way an open chain does.
That's what makes a closed loop so powerful on the hardest grids: one correctly-traced loop can cascade several eliminations at once, all from a single piece of reasoning. The trade-off is verification — a loop that isn't perfectly alternating all the way around produces false eliminations, so it needs to be checked link by link before you trust it.