Ciro Santilli @cirosantilli 40

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Cayley-Dickson construction Updated 2025-07-16

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Constructs the quaternions from complex numbers, octonions from quaternions, and keeps doubling like this indefinitely.

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Cayley graph Updated 2025-07-16

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You select a generating set of a group, and then you name every node with them, and you specify:

each node by a product of generators
each edge by what happens when you apply a generator to each element

Not unique: different generating sets lead to different graphs, see e.g. two possible en.wikipedia.org/w/index.php?title=Cayley_graph&oldid=1028775401#Examples for the

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CC BY-NC-ND 4.0 Updated 2025-07-16

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CC BY-NC-SA Updated 2025-07-16

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Too restrictive. People should be able to make money from stuff.

The definition of "commercial" could also be taken in extremely broad senses, making serious reuse risky in many applications.

Notably, many university courses use it, notably MIT OpenCourseWare. Ciro wonders if it is because academics are wary of industry, or if they want to make money from it themselves. This reminds Ciro of a documentary he watched about the origins of one an early web browsers in some American university. And then that university wanted to retain copyright to make money from it. But the PhDs made a separate company nonetheless. And someone from the company rightly said something along the lines of:

The goal of universities is to help create companies and to give back to society like that. Not to try and make money from inventions.

TODO source.

The GNU project does not like it either www.gnu.org/licenses/license-list.en.html#CC-BY-NC:

This license does not qualify as free, because there are restrictions on charging money for copies. Thus, we recommend you do not use this license for documentation.
In addition, it has a drawback for any sort of work: when a modified version has many authors, in practice getting permission for commercial use from all of them would become infeasible.

en.wikipedia.org/wiki/Creative_Commons_NonCommercial_license#Defining_%22Noncommercial%22 also talks about the obvious confusion this generates: nobody can agree what counts as commercial or not!

In September 2009 Creative Commons published a report titled, "Defining 'Noncommercial'". The report featured survey data, analysis, and expert opinions on what "noncommercial" means, how it applied to contemporary media, and how people who share media interpret the term. The report found that in some aspects there was public agreement on the meaning of "noncommercial", but for other aspects, there is wide variation in expectation of what the term means.

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CCFv3 Updated 2025-07-16

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Announcement: alleninstitute.org/news/a-new-high-resolution-3d-map-of-the-whole-mouse-brain/