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Configurations

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What is the relationship between an arrangement of lines and a projective configuration? -- Cheers, Steelpillow (Talk) 12:38, 22 November 2009 (UTC)[reply]

I think it would be helpful to add a brief explanation to both articles, and cross-link. -- Cheers, Steelpillow (Talk) 13:03, 22 November 2009 (UTC)[reply]
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Definition section

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The article looks very well done, as might be expected from an editor who has published in the field. Unfortunately, I don't have time at present to give a good review. But on the definition section,

  • It seems light on citations--none for the definition itself?
  • There could be more explanation of concepts and/or wikilinks. Perhaps a digram to illustrate the concepts?
  • As an intro section, the definition section uses fairly high-level concepts that may baffle readers coming from a high-school geometry understanding of the topic. For instance, they might wonder what is an unbounded convex polygon, and if they make the association of that with what you are talking about, how is a wedge of the plane going off to infinity even considered a polygon?

Building a pedagogical transition from an elementary-looking problem to state-of the art understanding is often difficult, but the intro section could benefit from a bit more of an on-ramp. {{u|Mark viking}} {Talk} 19:23, 29 January 2024 (UTC)[reply]

The entire first paragraph, and its embedded three bullet points, have a single source, because that source was adequate for those definitions. If you think[1] that[1] adding[1] lots[1] of fnords[1] would give readers[1] warm[1] fuzzy[1] feelings[1] then[1] I suppose[1] we could repeat[1] that one footnote[1] multiple[1] times.[1] —David Eppstein (talk) 21:35, 29 January 2024 (UTC)[reply]

Image Examples

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Hi @David Eppstein I appreciate all the wonderful images you make for WP. For the more elementary reader I suggest that the first image is edited such that there is one example of isomorphic arrangements and a small edit to that arrangement to make it not isomorphic. This is will make it more clear to readers that have not encountered isomorphism.

"Two arrangements are said to be isomorphic or combinatorially equivalent if there is a one-to-one boundary-preserving correspondence between the objects in their associated cell complexes."

Then this quote can indicate the image is expository.

Also the current caption on the first image does not make sense to a new reader who has never seen the word simplicial. Some blue text is in order? Czarking0 (talk) 15:06, 2 June 2024 (UTC)[reply]

The first image was really created for a different purpose: it shows a complete quadrangle and complete quadrilateral respectively. But also it shows the difference between simple arrangements and non-simple arrangements, a distinction that I think may be more fundamental than isomorphism here.
The caption describes two terms defined inside this same article. —David Eppstein (talk) 16:43, 2 June 2024 (UTC)[reply]

Practical applications

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I'm wondering if this article should include some practical examples of how "Arrangement of lines" is used in computer graphics and robotics. E.g., Computer graphics:

  • Rendering and ray tracing: In ray tracing, an algorithm traces the path of light as lines (rays) to simulate the way light interacts with objects. Arrangements of lines help in efficiently determining intersections and rendering realistic scenes.
  • Hidden line removal: In 3D modeling and rendering, arrangements of lines are used to determine which edges of a 3D object are visible and which are hidden from the viewer’s perspective. This technique enhances the clarity and realism of the rendered image.

Robotics:

  • Path planning: In robotics, line arrangements are needed for path planning, where the robot must navigate through an environment with obstacles. The robot's sensors often detect lines that represent walls or other barriers, and efficient algorithms are needed to find a collision-free path.
  • Motion planning: For robotic arms, especially in manufacturing, line arrangements help in determining the sequence of movements needed to avoid collisions and achieve precise positioning of the end effector.

I'm not an expert in either mathematics or these applications (so am unsure how relevant this is to the topic) but thought I'd throw it out there in case it might be useful. Esculenta (talk) 14:52, 19 June 2024 (UTC)[reply]

For one thing, the situations you describe are three-dimensional, but the arrangements discussed in this article are two-dimensional. And vague allusions to vaguely related practical problems are too common in the research literature, but not helpful here. My understanding is that the main practical connection is through point-line duality, as is already briefly mentioned in connection with one practical problem, the computation of the Theil–Sen estimator. —David Eppstein (talk) 18:23, 19 June 2024 (UTC)[reply]
Understood on the 2-D arrangements. How about point-line duality and Voronoi diagrams?
In computational geometry, line arrangements are used in the construction and optimization of Voronoi diagrams, which are extensively used for spatial analysis in geographic information systems (GIS) and computer graphics. For example, algorithms for constructing Voronoi diagrams often use line arrangements to efficiently manage and partition space, optimizing tasks such as nearest-neighbor queries and spatial indexing. Esculenta (talk) 05:13, 20 June 2024 (UTC)[reply]
In what sense do you think "line arrangements are used in the construction and optimization of Voronoi diagrams"? "Used", how? What is your published source for them being used in this way? —David Eppstein (talk) 05:39, 20 June 2024 (UTC)[reply]
As one example, doi:10.1007/BF01840357. Fortune's sweep line algorithm uses line arrangements to manage the "beach line" (a collection of parabolic arcs that changes dynamically) status and handle events efficiently during the sweep. This process can be viewed as managing the intersections and arrangements of lines and parabolas, which is directly related to the study of line arrangements. This connection between line arrangements and Voronoi diagrams helps optimize nearest-neighbor queries and spatial indexing, and demonstrates a practical application of line arrangements in computational geometry. (some notes here). Esculenta (talk) 15:27, 20 June 2024 (UTC)[reply]
Are you an AI? You are writing technical words in an order that suggests that they have some meaning that is not present in the sources you cite. There are no line arrangements in the beach line. It is the boundary of a union of parabolas. —David Eppstein (talk) 18:54, 20 June 2024 (UTC)[reply]
My mistake, I conflated line arrangement with the boundary of a union of parabolas, thanks for the correction. Esculenta (talk) 19:36, 20 June 2024 (UTC)[reply]

GA Review

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GA toolbox
Reviewing
This review is transcluded from Talk:Arrangement of lines/GA1. The edit link for this section can be used to add comments to the review.

Nominator: David Eppstein (talk · contribs) 02:48, 29 January 2024 (UTC)[reply]

Reviewer: Electrou (talk · contribs) 09:50, 8 October 2024 (UTC)[reply]


Article is clear and concise, no original research, no plagiarism, follows the Manual of Style guidelines, contains reliable sources and inline citations. I think it should have good article status.

@Electrou: Thanks, but should I expect a detailed review to come? The short text above does not meet the expected standards of depth and source checking for a review and you have also not followed the post-review steps from Wikipedia:Good article nominations/Instructions. As this appears to be your first GA review, perhaps Wikipedia:Good article mentorship would be helpful? —David Eppstein (talk) 21:35, 14 October 2024 (UTC)[reply]
Yes Electrou (formerly Susbush) (talk) 18:43, 17 October 2024 (UTC)[reply]
Comment: Are you planning on reviewing this? Because other people would be willing to take it up for review, if you aren't gonna do it. DoctorWhoFan91 (talk) 05:54, 26 October 2024 (UTC)[reply]

Crisco 1492

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Image review

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  • File:Complete-quads.svg mentions quads, but not the involvement of lines. This may be confusing (well, for me is confusing) for lay readers clicking through. Licensing looks good.
    • You mean, on the image description page? WP:GACR discusses only licensing and captions. The image description page also provides a link to Complete quadrangle which explains the involvement of lines for readers clicking through. If a reader clicks through once, doesn't click through a second time, and doesn't directly see the lines in the image, I'm not sure what more to do. —David Eppstein (talk) 03:53, 30 October 2024 (UTC)[reply]
      • You are correct that the link between the quadrangle and lines is implied. That being said, as we are using the image to illustrate lines, not quadrangle, and although the caption in the article notes the value of the arrangement the image description does not currently support this point. This speaks to MOS:IMAGEREL, which is part of GACR. Adding "the complete quadrangle offers a simplicial arrangement of lines, while the complete quadrilateral offers a simple line arrangement" would help make the relevance explicit.  — Chris Woodrich (talk) 00:20, 3 November 2024 (UTC)[reply]
  • File:Decagon simplicial arrangement.svg - Looks good
  • File:Roberts triangle theorem n=7.svg - Looks good
  • File:17KobonDreiecke.svg - Don't think PD simple really covers it. The discussion of the threshold of originality in Germany on Commons notes some things such as a triangular-based patio table as attracting copyright; consequently, the TOO may be quite low. If this was created by a user, ideally it should have a CC license.
    • The link you give states "the aesthetic effect of the article can only provide a basis for copyright protection to the extent that it is not dictated by the article's utilitarian purpose". The only part of this figure not dictated by the utilitarian purpose of describing a mathematical construction (the 17-line Kobon triangle problem solution) is the choice of what color to use to shade in the triangles. —David Eppstein (talk) 03:53, 30 October 2024 (UTC)[reply]
      • Is there only one 17-line solution to this problem? If not, a strictly utilitarian argument doesn't really hold weight. I note, for example, that the five line, five triangle solution in our article on the Kobon triangle problem is presented in two forms, with slightly different angles, and one with line segments rather than lines. This speaks to the possibility of a creative element beyond the colour.  — Chris Woodrich (talk) 00:20, 3 November 2024 (UTC)[reply]
  • File:Tiling Dual Semiregular V4-8-8 Tetrakis Square.svg - Looks good
  • File:Tiling Dual Semiregular V4-6-12 Bisected Hexagonal.svg - Looks good
  • File:Tiling Regular 3-6 Triangular.svg - Looks good
  • File:Pappos pseudo.svg - Licensing looks good
  • File:Ageev 5X circle graph.svg - Looks good, though my first impression was a "web of things" depiction of species and their interrelations... although, I see the caption mentions five colours but I'm only seeing one. Is this deliberate?
    • Sort of. The point of this construction was not so much to find something that could be colored with five colors (that would be true of any such arrangement with no three mutually crossing arcs) but rather to find something for which there is no way of coloring it with four colors. It is not easy to depict "cannot be colored with four colors". Showing it with five colors should not suffice to convince anyone that fewer colors is impossible.
  • Not a GA criterion, but I think the explanation would definitely benefit from some sort of animation. File:Missing Square Animation.gif offers an excellent example of what could be done with animations.
    • I have very little experience or available software setup for making animations. I'm much more comfortable with stills and svg-format vector images. And I don't think Wikimedia can handle animated svgs. But I think the only description that involves anything changing over time is the part about the incremental construction algorithm. Is that the one you meant? If a suitable animation has already been uploaded by someone else I'd be happy to include it.

Prose review

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  • As I mentioned at WP:GAN, the lede is inadequate to explain all elements of the article subject. Not being a maths guy, I can't really help with that, but referring to FA examples like Parity of zero and Euclidean algorithm, the lede should be simple enough that even a schlub like me can get the gist of it. So, for example, I'd recommend including the main categories of line arrangement, some overview of non-Euclidean arrangements vis-a-vis Euclidean ones, etc. Since this would mean a whole new lede, I'm not going to review the text yet.
  • Overall, to help the lay reader, I'd add more links to the text. For example, polygon may be a common word, but since it is part of the crux of this definition, a link will definitely be beneficial. Other beneficial links include line segments, rays, vertice, convex region,
  • Intuitively, - Okay in a journal, but probably not on Wikipedia
    • Do you have a similarly-concise replacement wording for "the following description is intended to appeal to the reader's visual intuition but is not rigorous mathematics"? —David Eppstein (talk) 23:51, 2 November 2024 (UTC)[reply]
      • No. However, I do feel that intuitively would fall under the words to watch part of the MOS. If the adverb were omitted, would this be detrimental to the definition?  — Chris Woodrich (talk) 00:22, 3 November 2024 (UTC)[reply]
        • If you think that this part is mathematical definition, rather than intuition to help you understand the definition that is coming next, then this word has failed in its purpose. But "intuition" or variant forms of the same word is indeed a standard technical term for this part of a mathematical explanation; see e.g. this academic paper entitled "intuitive explanations in mathematical education". (Not to be confused with intuitionism.) Google Scholar has nearly 7000 hits for "mathematical intuition" including 145 where that phrase is part of the title. —David Eppstein (talk) 01:14, 3 November 2024 (UTC)[reply]
          • I did not say that I saw it as part of the definition. My concern was that using the adverb could be understood to "indicate particular interpretive viewpoints", as per the wording of the MOS section I cited. Referring to each of the current maths FAs, I am not seeing the word in any of its forms used in Wikipedia's voice. I am seeing it book titles and quotations from other works. Consequently, I feel it best to ask for a second opinion about the use of this adverb. — Chris Woodrich (talk) 01:25, 3 November 2024 (UTC)[reply]
            • Anyway, since this word appears to be conveying the incorrect and unintended impression that it is expressing an opinion about the content, rather than conveying the intended meaning that the following text is informal and intended to make the formal part that follows easier to understand, I have rewritten that part to call it "an informal thought experiment". It is wordier but maybe will provoke fewer such misunderstandings. —David Eppstein (talk) 01:27, 3 November 2024 (UTC)[reply]
              • Perhaps. I am going to note here that, when I consulted the cited source, I saw Grunbaum doesn't use such a thought experiment. He identifies on Page 2 that the material being covered is easy enough for a graduate student, which explains why he goes straight into the definitions on Page 4. As such, as it currently stands the thought experiment is not explicitly provided by a source. It does follow from what the sources indicate, and thus I think it still meets criterion 2b. ("All content that could reasonably be challenged, except for plot summaries and that which summarizes cited content elsewhere in the article, must be cited no later than the end of the paragraph") — Chris Woodrich (talk) 01:42, 3 November 2024 (UTC)[reply]
                I am not sure I can help this, but is the phrase "roughly speaking" might help? Thought I don't mind to use "intuitively" or "by intuition" to say something informal thought experiment. Dedhert.Jr (talk) 02:13, 4 November 2024 (UTC)[reply]
                I do think "roughly" or even "approximatively" better suits the letter of the MOS. — Chris Woodrich (talk) 12:15, 4 November 2024 (UTC)[reply]
                Maybe, but I think both are a distortion of the intended meaning. —David Eppstein (talk) 17:50, 4 November 2024 (UTC)[reply]
  • of the arrangement are isolated points belonging to two or more lines, where those lines cross each other - Worth including the word "intersection" somewhere, or does that have a definition in maths that doesn't really fit this context?
    • If you have already formalized lines as being certain sets of points, then yes, each vertex is the unique element of the set of points formed by intersecting some two lines. Often the step of going from a one-element set to the unique member of the set is skipped over and people will say that a point is the intersection of two lines, but that language is a bit sloppy. And using sets is not necessary: it is possible and in many cases helpful to think of lines as indivisible objects and to think of point-line incidence being a binary relation rather than as membership in a set. —David Eppstein (talk) 23:56, 2 November 2024 (UTC)[reply]
  • locally finite - per WP:EMPHASIS, we should not add italics for emphasis. Previous instances were words as words, whereas this one is not a definition.
  • The same classification of points, and the same shapes of equivalence classes, can be used for infinite but locally finite arrangements, in which every bounded subset of the plane may be crossed by only finitely many lines, although in this case the unbounded cells may have infinitely many sides. - May be easier to read if split into at least two sentences
  • The study of arrangements was begun by Jakob Steiner, who proved the first bounds on the maximum number of features of different types that an arrangement may have. - When? How long have the properties of line arrangement been discussed by mathematicians? Your reference has a year, but nothing is mentioned in the running text. We may not have an entire history section like Euclidean algorithm, but it is good to have a rough idea as to how the discourse has emerged and developed.
  • Any arrangement can be rotated to avoid axis-parallel lines, without changing its number of cells. - Is that comma necessary?
  • infinite-downward rays - Not sure I follow; if a ray is itself infinite, how can it have direction? Or does "downward" mean something else in this context?
  • Again, this worst-case bound is achieved for simple arrangements. - Not feeling this one. You use "bound" for cell boundary above, but here we are talking about edges. Also, "again" and "worse-case" feels more like essay language than Wikipedia language. Would something like "A value of at most is achieved in simple arrangements" be accurate?
  • The best upper bound ... the best lower bound - How are bounds supposed to be "best" (or worst, as above)?
    • I added the word "known" to make more clear that this reflects our state of knowledge rather than some notion of being mathematically impossible to improve. Anyway, a bound is better when it is closer to the thing it bounds. So an upper bound is better when it is smaller than some other upper bound, and a lower bound is better when it is larger than some other lower bound. But using minimum/maximum type words in alternation tends to be a bit confusing, so I didn't want to say "the least known upper bound" and "the greatest known lower bound", especially when those are so close to phrases like least upper bound and greatest lower bound that have a different and more technical meaning. —David Eppstein (talk) 05:42, 5 November 2024 (UTC)[reply]
  • I'm seeing other uses of "bound" for maxima and minima. Again, given the use of "bound" to also refer to the boundary of the cell, I'm wondering if an alternative phrasing may be easier to follow.
  • By Melchior (1940) - Per WP:PAREN, parenthetical referencing has been deprecated. I know that strictly speaking this is more of a "mention" than a parenthetical reference, but perhaps "by Eberhard Melchior in 1940" would work better.
  • Another parenthetical citation in #Triangles in arrangements
    • In this one, it's more obviously article text, not a citation, because there's a footnote to the same reference (the actual citation) at the end of the same sentence. But I'm not convinced that the author names and dates are necessary in the article text, so I removed them. —David Eppstein (talk) 05:51, 5 November 2024 (UTC)[reply]
  • the minimum number of triangles is n-2, by Roberts's triangle theorem. - Feels like this could be expressed more clearly
    • I'm not sure what's unclear here. For Euclidean arrangements, every arrangement must have at least n-2 triangles, and there exist arrangements with exactly n-2 triangles. Therefore the minimum is n-2, rather than some other number. This is in contrast with the two previous sentences, which stated the same sort of thing for projective arrangements but with n instead of n-2. —David Eppstein (talk) 05:55, 5 November 2024 (UTC)[reply]
  • For non-simple arrangements the maximum number of triangles is similar but more tightly bounded - Not understanding what "more tightly bounded" is meant to imply in this situation. A bit of clarification could help.
  • For some but not all values of n - A lay reader may think that n and n(n-2)/3 are part of the same equation. Reframing this sentence would help.
  • Another parenthetical in #Multigrids and rhombus tilings
  • families of parallel lines this construction just gives the familiar square tiling of the plane, and for three families of lines at 120-degree angles from each other (themselves forming a trihexagonal tiling) this produces the rhombille tiling - "just" and "familiar" could be nixed without affecting the meaning
  • Constructing an arrangement means, given as input a list of the lines in the arrangement, computing a representation of the vertices, edges, and cells of the arrangement together with the adjacencies between these objects, for instance as a doubly connected edge list. - Might be easier to parse if separated into two sentences.
  • Due to the zone theorem, - Is it a causal relationship, as implied by due, or is this per the zone theorem?
  • However, the memory requirements of this algorithm are high, so it may be more convenient to report all features of an arrangement by an algorithm that does not keep the entire arrangement in memory at once. - Given that this paper is from 1989, is the claim about memory requirements still applicable?
    • I'm sure it depends on the application. It's more a matter of how it scales than absolute numbers. If for some reason you wanted to compute arrangements with millions of lines, the time might still be possible but the space of computing the whole arrangement wouldn't be. But the claim of being "more convenient" and "more efficiently" is kind of an inappropriate editorialization (I think more than some of the other ones you've complained about earlier) so I replaced this by a more factual statement merely about the space being lower. —David Eppstein (talk) 07:33, 6 November 2024 (UTC)[reply]
  • but the general problem remains open. - citation needed
    • It's kind of difficult to source a negative (this problem hasn't been solved yet) but I added a 2020 reference stating it as still open, much more recent than the other references in this part. It's a master's thesis, though, which you might object to. —David Eppstein (talk) 07:43, 6 November 2024 (UTC)[reply]
  • Pseudoline arrangement and arrangements of hyperbolic lines are bolded, which doesn't really segue with the rest of the discussion in the article.
    • For the hyperbolic lines, I think this is fair, and I unbolded it. But pseudoline redirects to this section; see Wikipedia:Manual of Style/Text formatting § Article title terms "This is also done at the first occurrence of a term (commonly a synonym in the lead) that redirects to the article or one of its subsections, whether the term appears in the lead or not". The whole phrase "pseudoline arrangement" is bolded rather than just "pseudoline" because it does not make much sense to talk about a curve as being a pseudoline outside the context of a system of other curves with which it forms a pseudoline arrangement. —David Eppstein (talk) 07:48, 6 November 2024 (UTC)[reply]
  • Another parenthetical ref in #Non-Euclidean line arrangements
    • In the caption? It's not really a reference (none of the captions currently have references), just a textual description of the context from which this arrangement comes. In this context it makes less sense to expand it out into a longer and unparenthesized form merely for the sake of avoiding parenthesized text because some editors had a bee in their bonnet about articles that formatted their references parenthetically rather than in footnotes and agreed to deprecate that syntax for actual references in an RfC that was on a discussion page for how to format references (not the MOS for how to write article text). Captions should be concise. Do you maybe have a similarly-concise way of saying the same thing with a different syntax?

Source review

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  • I see that you cite four of your own publications. Given the number of references to other mathematicians, as well as the fact that the article is built predominantly on their work, I do not think that this falls afoul of WP:COI.
    • Thanks. I try not to cite my own publications when something else will suffice, but I'm not sure that's true in this case. The E/Falmagne/Ovchinnikov book is the most replaceable, but even for it I don't know where to find a similar discussion of the varied definitions of pseudolines (except a blog post also by me on the same thing, on which I based that content in the book, and I try more strongly to avoid citing my blog). —David Eppstein (talk) 07:56, 6 November 2024 (UTC)[reply]
  • All of the references in #Algorithms are at least twenty years old. Given the emphasis on computer-assisted mathematics in this section, and the advances in computing in this time frame (based on a quick Google search, my tower has north of ten thousand times more flops than a CRAY-1), it would be beneficial to have more recent references.
    • One doesn't generally need to find new algorithms merely because one is using a faster computer. And many of the basics are long settled. But I found and added three recent algorithms in the footnotes for the middle paragraph of this section. —David Eppstein (talk) 08:31, 6 November 2024 (UTC)[reply]
  • Based on my understanding of the article, the focus is on discussion of line arrangement in planes (i.e., two-dimensional spaces). Is there literature on line arrangements in n dimensions, or is that covered under the hyperbolic arrangement?
    • There is a qualitative difference between lines in 2d and in higher dimensions: in 2d, they split the plane into cells, but in higher dimensions the free space is all one piece, and disjoint lines can be moved continuously from any system of positions to any other system of positions. It's the same for points in 1d vs in higher dimensions. Instead, the closest analogous concept in higher dimensions is Arrangement of hyperplanes, something we have a (linked) separate article for. One can still study lines in higher dimensions. I think there is also some study of complex lines (that is, spaces coordinatized by a single complex number) in 3-dimensional complex spaces (coordinatized by triples of complex numbers) hinted at in quadrisecant but I think this would be a little esoteric for a mention in this article, except maybe as a see-also link if we had an article to link to. —David Eppstein (talk) 08:31, 6 November 2024 (UTC)[reply]
  • Your use of page numbers is not standardized. Refs 1 through 3 use them, and a couple others, but most everything is a whole-article reference. Page numbers would help verifiability.
    • The intent was to cite specific page numbers in books, and for citations to specific claims mentioned in passing in article references, but not to repeat the whole page range for articles that are largely or entirely about the cited claim. I added pages for several more footnotes according to this criterion. Leighton really should have a page number but I do not have a copy from which I can obtain this, and very many other sources just cite Leighton as the standard reference for this claim without further specifics. Grünbaum 1972 also should have pages, but I don't have access to this at home. I'll check later whether I have a physical copy in my office. —David Eppstein (talk) 02:12, 7 November 2024 (UTC)[reply]
  • "Sequence A000124 (Central polygonal numbers (the Lazy Caterer's sequence))" stands out as the only non-SFN in the article. I'd convert it to an SFN reference as well, just for the sake of uniformity.
  • Some of your references are in title case, while others are in sentence case. Per MOS:REF, we should be consistent.
    • The intended convention is to use italic-font title case (most words capitalized) for titles of journals and books, and upright-font sentence case (capitals only for the first word, the first word after a colon, proper nouns, and German nouns) for titles of articles in journals and books. A quick scan found two books (and the new master's thesis) not following this convention; fixed. I suppose you're aware that the GA rule about reference formatting does not actually require consistency of formatting, but that is something I like to do anyway. —David Eppstein (talk) 00:07, 7 November 2024 (UTC)[reply]
  • Earwig doesn't see anything to worry about.
  • Spotcheck, using this revision as a basis.
    • [4] - Not quite what the source says. Source says Steiner was perhaps the first, waffling in case an earlier paper existed.
    • [5] - Not going to lie, I don't see the exact formula rendered here. That being said, I'm aware it may be rendered differently and I don't have the baseline knowledge to see it. The fact that simple arrangements achieve the maximum bound is supported
      • This comment refers to the first bullet of "Complexity of arrangements", now footnote [4] after moving the history caused some renumbering. The reference gives a formula for the number of cells of a variable dimension in an arrangement of variable dimension. Plugging in cell dimension k=0 and arrangement dimension d=2, one gets a sum with a single term i=0, for which the term is (2 choose 0)(n choose 2). This simplifies to the given formula by observing that (2 choose 0)=1. I think this falls under WP:CALC: this simplification is a trivial calculation if only one is familiar with the notation used by the source and how to apply it to this specific case. As WP:CALC recommends, I added a note to the footnote explaining the calculation. —David Eppstein (talk) 08:22, 8 November 2024 (UTC)[reply]
  • Other spotchecks are currently hindered by the lack of page numbers, as well as my own limitations as a lay reader.  — Chris Woodrich (talk) 16:39, 31 October 2024 (UTC)[reply]

Conclusion

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