Category talk:Images with rotational symmetry

Categorization of images without mirror symmetry as chiral

Copied from Commons:Administrators' noticeboard/User problems/Archive 60

TL;DR: Watchduck got the meaning of "chiral" wrong and made a wrong redirect. "Being chiral" aka "lacking mirror symmetry" could be used as a property for the categorization of images, but currenty it is not.

Could anybody investigate this user producing numerous edits to image description pages and categories? A person making such things shouldn’t do categorization (note that an explicitly worded notice about opposition to Category: Images with dihedral symmetry was present), whereas I don’t edit wikis actively anymore, hence won’t participate. Incnis Mrsi (talk) 17:50, 8 October 2016 (UTC)

I don't mind if someone looks into categorization work I have done. (User:Watchduck/cat is a place where some of my work is mentioned.) But I would like to mention, that the situation I had found here was much more convoluted than what I normally encounter and deal with.

There was a note that "Chiral images with rotational symmetry" "is opposed to" Category: Images with dihedral symmetry and its subcategories. What is that supposed to mean? If something has chiral and rotational symmetry, it has dihedral symmetry. So the name was counterintuitive, and there was no further explanation. What is "is opposed" supposed to mean? How about an example what belongs in this but not in the other category? Needless to say, that the images in this six years old category had nothing in common that those in Category: Images with dihedral symmetry did not also have in common. Watchduck (quack) 19:10, 8 October 2016 (UTC)

@Watchduck: Open any damn dictionary and look for the word “chiral[ity]”. Then open any damn encyclopedia and read what the “dihedral group” is. Incnis Mrsi (talk) 19:13, 8 October 2016 (UTC)

You seem to imply, that "Chiral images with rotational symmetry" is a perfectly self-explaining name. Maybe you could just assume for a moment that it is not, and give us some examples of images that are chiral with rotational symmetry, but do not have dihedral symmetry. I do not doubt that what you are saying makes sense, I just doubt that it is self-explaining. And I can assure you, that the category was a mess anyway, and that there was the same kind of content as in the other one. Watchduck (quack) 19:35, 8 October 2016 (UTC)

I seem to imply that images (as well as subcats) from Category: Chiral images with rotational symmetry were indeed chiral, whereas images (and subcats) from Category: Images with dihedral symmetry were not chiral. Now the latter category and its descendants are, obviously, contaminated and dislocated by Randy edits like this (possibly already not so, 08:10, 10 October 2016 (UTC)). Again, chirality is the antonym to mirror symmetry. For whom on Earth was it counterintuitive?! Now all the Commons can see how Watchduck engages in pointless sophistry instead of apologies for disruption and starting to fix the damage. Should one entrust him categorization of images and, especially, maintaining the categories’ structure? Incnis Mrsi (talk) 20:20, 8 October 2016 (UTC)

Honestly, I find this quite creepy. You wrote to a user, because you saw on my talk page (when you wrote me), that he had an argument with me before. I see this as an attempt to make this as personal and emotional as possible. Watchduck (quack) 19:58, 8 October 2016 (UTC)

I wrote to AnonMoos because trust him, and don’t know about your arguments, really. Incnis Mrsi (talk) 20:06, 8 October 2016 (UTC)

That category included things like Category:Triskelion, Category:Triple spiral, Category:Roundabout mandatory signs, , , or . No mirror symmetry here.
Anyway, I think I see for what kind of images you must have originally intended that category: Images like , or that have rotational symmetry, but are almost chiral. (One might define them as "things with rotational symmetry that throw a shadow with dihedral symmetry".) If you had written that on the category page, people might have used the category in the way you had intended. With proper restrictions ( but not ) it may be useful to put these images in their own categories, and I am willing to help.
But I maintain that my change was by no means a terrible one. What I have removed was not what you had intended it to be, but what it had become. Watchduck (quack) 20:47, 8 October 2016 (UTC)

I indeed should not have moved to 4-fold dihedral symmetry. I moved Borromean crosses to 2-fold dihedral symmetry now. Watchduck (quack) 13:29, 9 October 2016 (UTC)

This looks now some bit better. I don’t have a strong opinion how some specific things (such as Borromean crosses) should be categorized. May be a separate category of “things with rotational symmetry that throw a shadow with dihedral symmetry” is warranted, may be it isn’t… anyway, “chiral” was a valid classification property for rotationally symmetric pics where dihedral symmetry (= “¬chiral”) is rather ubiquitous but is missing dramatically from many important cases. Some efforts were applied to classify several categories and numerous separate images to either of two sides. Watchduck destroyed one of the branches, making no attempt to improve or duly discuss the chiral/dihedral point, until just now. Incnis Mrsi (talk) 16:31, 9 October 2016 (UTC)

Could you please just give some clear examples of images that are chiral with rotational symmetry (as opposed to having dihedral symmetry), and that in your opinion are currently miscategorized? Watchduck (quack) 16:57, 9 October 2016 (UTC)

They are not categorized now; this branch of categories is removed outright. There are some categories (e.g. Rotation symbols) where one could look for (some particular cases of) chiral rotationally symmetric images, but few such categories are accessible from Chirality, whereas under Images with rotational symmetry a surfer has no option related to chirality. Or am I missing something? Incnis Mrsi (talk) 07:55, 10 October 2016 (UTC)

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Some observations:
1) I would have come to this page whether I was summoned or not, since I'm going to open an unrelated case.
2) I'm not really an expert in the mathematics of symmetry, (as opposed to someone who has uploaded a lot of abstract images with different types of symmetry).
3) Incnis_Mrsi seems to have a consistent vision that the farther down something is in the category tree, the more symmetry it inherits. So Category:72-fold rotational symmetry is a subcategory of 36-fold rotational symmetry, 24-fold rotational symmetry, 18-fold rotational symmetry, 12-fold rotational symmetry, 9-fold rotational symmetry, 8-fold rotational symmetry, 6-fold rotational symmetry, 4-fold rotational symmetry, 3-fold rotational symmetry, 2-fold rotational symmetry etc. If User:Watchduck has a different vision, he needs to articulate it and express it.
4) A chiral image is one where reflecting it in the mirror results in an image which is different from the original, in the sense that no amount of rotation or moving (translation) of the flipped image will allow it to be superimposed over the original. Therefore, something with dihedral symmetry is by definition NOT chiral, while something with rotational symmetry without reflection symmetry IS chiral. Of course, something can be chiral without having any rotational symmetries at all (as in left-handed glove etc.)... AnonMoos (talk) 00:09, 10 October 2016 (UTC)

@AnonMoos: Not necessary [more] symmetry; just more specific categorization property. We’re discussing wanton disruptions under Category: Chiral images with rotational symmetry (namely, whether this particular property was helpful for classification), not special problems of nesting categories. Incnis Mrsi (talk) 07:48, 10 October 2016 (UTC)

Thanks to the comment by AnonMoos I actually understood the problem now. I was indeed wrong about the meaning of chiral. (Because two chiral objects are mirror symmetric, I had falsely equated chiral with mirror symmetric.) Sorry for that.

Anyway, the only actual difference that we have here is that I think that e.g. images with only 4-fold rotational symmetry should be directly in that category, and only categories like 4-fold dihedral symmetry or 8-fold rotational symmetry should be nested under it. You seem to want that no images are directly in 4-fold rotational symmetry, but that the ones that are not dihedral should also be in a nested subcategory 4-fold rotational symmetry only or Chiral images with 4-fold rotational symmetry. I generally don't think that "this but not that" categories are a great idea, but they can have their uses.

Concerning "They are not categorized now": I have simply moved images with only 4-fold rotational symmetry to that category and images with 4-fold dihedral symmetry to that one. I find the idea that everything that is not mirror symmetric ought to be categorized under Chirality a bit over the top, but why not... Watchduck (quack) 12:08, 10 October 2016 (UTC)

Darn, one of the images in w:Chirality (mathematics) was even added by me. Watchduck (quack) 12:39, 10 October 2016 (UTC)

How about looking what does a freaking category contain next time, before mass edits and making redirects? There is even safer rule: don’t touch when don’t understand. Incnis Mrsi (talk) 14:18, 10 October 2016 (UTC)

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Yes, the redirect was wrong. But contrary to the impression that is created here, I have not miscategorized anything. I have simply used the default way of categorizing things by the properties they have, rather than by the properties they don't have.
The consistent vision that the farther down something is in the category tree, the more symmetry it inherits makes perfect sense. It is also realized in a way that makes sense: Images that have only 6-fold rotational symmetry are directly in that category, while 6-fold dihedral or 12-fold rotational are nested below. What would not really make sense would be categories like 6-fold rotational symmetry (but not more than 6-fold) opposed to 12, 18, 24-fold rotational or 6-fold rotational symmetry (but no reflectional symmetry) opposed to 6-fold dihedral. Because we usually don't categorize by what something is not. The category I have removed was "Images with rotational but no reflectional symmetry", and I don't think we really need that - just like we probably don't need "Images with reflectional but no rotational symmetry". (We also don't have Non-Communist red stars or Non-Nazi Swastikas - although this exception exists.)
Anyway, I don't have a strong opinion on this. If there is consensus that not having reflectional symmetry aka Chirality should be treated like a property in it's own right, that's what we will have. But then we should also have proper subcategories like the beforementioned. Chirality contains mainly molecules and knots (and probably should contain Chiral polyhedra like the Snub cubes), but it would be very strange if all images without reflectional symmetry were in there. Watchduck (quack) 17:39, 10 October 2016 (UTC)

I was rather annoyed when "Category:Non-Nazi swastikas" was deleted -- I thought it served a quite useful purpose for years (see [1], [2]). The word "chiral" comes from the Greek stem for hand (χειρ-) and a Latin adjective suffix, and so is a fancy way of saying "handed" (as in "left-handed" etc.) AnonMoos (talk) 19:22, 10 October 2016 (UTC)

For the messy real world categories like Non-Nazi swastikas are quite unhelpful, I think. E.g. someone else may think that Hindu vs. Non-Hindu swastikas is the major distinction, and that would lead to complications. More importantly, some people may found a Hindu-Nazi organization and use swastikas, and then you have Hindu-Nazi swastikas both in Nazi and in Hindu swastikas - through which they would also be in Non-Nazi swastikas. When people are involved, better expect the unexpected.

But for mathematical topics the approach of partitioning a category into all possible subcategories from the very beginning can have some merit. E.g. for Polychora I would prefer a partitioning into convex/nonconvex, uniform/non-uniform, etc. But in this case I would find it consistent to go deeper in the category tree only when more symmetry is added.

BTW: I would prefer if 6-fold rotational would not directly contain 24-fold rotational, because that's already in there through 12-fold rotational. Technically this is over-categorization. To me it would seem enough when all of them (and not just the prime numbers) are in Rotational symmetry by order. Watchduck (quack) 23:18, 12 October 2016 (UTC)