confocaloid wrote: ↑February 18th, 2024, 12:47 am
Two 90-degree reflectors can make a perfectly valid 180-degree reflector.
In fact, the most natural (and hence least artificial) way of building 180-degree reflectors I can see, is to connect two small 90-degree reflectors (e.g. two Snarks, or two bumpers, or a bumper or a bouncer).
I think any 180-degree rotationally symmetric single-glider loop can be naturally described as a shuttle. (Including rectifier loops,
NW-2T16 reflector loops, four-Snark loops.)
Of course, shuttles that are too narrow to be made into loops (including "same-lane" shuttles) are shuttles too.
I definitely agree with everything in the above quote, except for the "too narrow to be made into loops" part. That seems like an arbitrary extra condition for loop-ness, so please can we just drop that extra criterion? For any case wider than the degenerate width-0 case, the center of a shuttled glider travels in a loop -- back on one lane and forth on a different lane.
I didn't explain "artificially" very well, in
dvgrn wrote: ↑February 17th, 2024, 12:50 pm
A) there's no "back and forth" going on here (unless two 90-degree reflectors get artificially classified as a 180-degree reflector, at least!)
This was related to the "back and forth" wording in
Loop (disambiguation). I'd like to keep that wording where it is, because there doesn't seem to be any broad agreement that that is an error.
The point that I was trying to make was that the p720 glider loop example from my last quote
could corrrectly be described as
"two 180-degree reflectors, with a glider shuttling back and forth between them".
But that's a bit artificial, because there's no reason to ignore the composite structure of the 180-degree reflectors. It seems more natural to describe the pattern as
"four 90-degree reflectors, with a glider traveling round and round between them", or
"four 90-degree reflectors, with a glider traveling in a loop between them".
Current status
If there's eventually a community consensus that Jubjub shuttles et al. are too narrow to count as loops, then it might make sense to put something on the LifeWiki about specifically excluding that
degenerate width-0 case from being a loop.
For the moment, there seems to be some disagreement even about excluding width 0, and any width wider than that definitely looks like a loop to some people.
That just means that the claim that, e.g., a pentadecathlon shuttle is not a glider loop (as well as being a shuttle) ... is controversial at the moment. That being the case, I'm thinking that existing LifeWiki contents can mostly just stay the same for the time being, since they currently don't seem to claim much of anything about whether glider shuttles count as glider loops.
I'd like to hear from anyone else who thinks that referring to Jubjub shuttles as, e.g., "adjustable glider loops", is either a bad idea or a good idea. It's still possible that a community consensus might develop on whether it's too confusing to include Jubjub shuttles as the "degenerate width-0" case in the glider-loop category.