Sun, 02 Dec 2018
There are combinatorial objects called necklaces and bracelets and I can never remember which is which.
Both are finite sequences of things (typically symbols) where the
start point is not important. So the bracelet ABCDE is considered
to be the same as the bracelets BCDEA, CDEAB, DEABC, and
EABCD.
One of the two also disregards the direction you go, so that
ABCDE is also considered the same as EDCBA (and so also DCBAE,
etc.). But which? I have to look it up every time.
I have finally thought of a mnemonic. In a necklace, the direction is important, because to reverse an actual necklace you have to pull it off over the wearer's head, turn it over, and put it back on. But in a bracelet the direction is not important, because it could be on either wrist, and a bracelet on the left wrist is the same as the reversed bracelet on the right wrist.
Okay, silly, maybe, but I think it's going to work.
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