This is particularly important in SQL: Nested set model in SQL, as it is an efficient way to transverse trees there, since querying parents every time would require multiple disk accesses.
The ASCII art visualizations from stackoverflow.com/questions/192220/what-is-the-most-efficient-elegant-way-to-parse-a-flat-table-into-a-tree/194031#194031 are worth reproducing.
As the sets:
__________________________________________________________________________
| Root 1 |
| ________________________________ ________________________________ |
| | Child 1.1 | | Child 1.2 | |
| | ___________ ___________ | | ___________ ___________ | |
| | | C 1.1.1 | | C 1.1.2 | | | | C 1.2.1 | | C 1.2.2 | | |
1 2 3___________4 5___________6 7 8 9___________10 11__________12 13 14
| |________________________________| |________________________________| |
|__________________________________________________________________________|Consider the following nested set:
0, 8, root
1, 7, mathematics
2, 3, geometry
3, 6, calculus
4, 5, derivative
5, 6, integral
6, 7, algebra
7, 8, physicsPreviously on EdX: www.edx.org/learn/quantum-physics-mechanics/delft-university-of-technology-topology-in-condensed-matter-tying-quantum-knots "DelftX: Topology in Condensed Matter: Tying Quantum Knots".
But then they regained their sanity and put the source code on GitHub: github.com/topocm/topocm_content and is CC BY-SA.
- Google Maps download offline maps. This works very reliably, you can select the area you want to download. The only downside is that Google maps can't reliably show a route offline, and it does not contain national cycle route routes. Or those features are impossible for a software engineer to get working after trying for about 2 hours.
- OpenStreetMap on browser with cycling layer: www.openstreetmap.org/#map=5/49.582/1.934&layers=C This is the best visualization of cycling routes I've found so far, contains both National Cycle Network and National Byway and a few others, and they are shown extremely clearly. But as a website it doesn't reliably work offline
- the OsmAnd app for Android is the best offline free-ish OpenStreetMap viewer I've found so far. You only have to pay after reaching 5 region downloads, and it is very cheap if you want to do so. The cycle route view is not amazing, the routes are not so clearly marked and mixed with very similarly colored big roads, but with a bit of effort you can make them out. No routing though
- I've heard Komoot can keep a predefined route (possibly auto planed) reliably offline, but haven't used it myself. I was not able to see National Cycle Route clearly marked anywhere on it
- github.com/google-deepmind/pushworld 2023 Too combinatorial, gripping makes it so much easier to move stuff around in the real world. But cool nonetheless.
Base machinery of the nervous system.
If any of you ever read this, do send me an email to Ciro Santilli saying hi and we can agree on a clear separation of usernames.
Although if you are just starting out, maybe you should just go from scratch with a unique Internet alias.
A younger unrelated Argentinian homonym who likes soccer that can be found through Google:Ciro used to like playing soccer too! :-)
- twitter.com/ciro_santilli
- www.facebook.com/profile.php?id=100009065024069
- www.instagram.com/ciro.santilli/ contains a few cool-sexy-boy-selfies as of 2025 when he hit that stage
- www.youtube.com/@cirosantilli9603
- www.linkedin.com/in/ciro-santilli-bb77b72b7
www.ancestry.com.au/genealogy/records/ciro-santilli-24-bkmssg documents a "Ciro Santilli" born 31 Jan 1887 at Castelvécchio in Subéquo, L'Aquila, in the Abruzzo region, just like Ciro Santilli's ancestors. Parents Francesco Santilli and Anna Silveri. The page also mentions:
- Ciro Santilli found in New York, Passenger and Crew Lists (including Castle Garden and Ellis Island), 1820-1957
- Ciro Santilli found in Oregon, Naturalization Records 1865-1991
CIA 2010 covert communication websites Wayback Machine CDX scanning by 
Ciro Santilli 37 Updated 2025-07-16
Ciro Santilli 37 Updated 2025-07-16The Wayback Machine has an endpoint to query cralwed pages called the CDX server. It is documented at: github.com/internetarchive/wayback/blob/master/wayback-cdx-server/README.md.
This allows to filter down 10 thousands of possible domains in a few hours. But 100s of thousands would be too much. This is because you have to query exactly one URL at a time, and they possibly rate limit IPs. But no IP blacklisting so far after several hours, so it's not that bad.
Once you have a heuristic to narrow down some domains, you can use this helper: ../cia-2010-covert-communication-websites/cdx.sh to drill them down from 10s of thousands down to hundreds or thousands.
We then post process the results of cdx.sh with ../cia-2010-covert-communication-websites/cdx-post.sh to drill them down from from thousands to dozens, and manually inspect everything.
From then on, you can just manually inspect for hist on your browser.
Ciro Santilli has sometimes wasted time with low impact projects such as those listed at Ciro Santilli's minor projects instead of doing higher impact projects such as those mentioned at: Section "The most important projects Ciro Santilli wants to do".
But maybe "Everything you did brought you where you are now." applies, maybe it is during the "low impact activities" that one gets the inspiration and experience required for the "high impact ones".
Pinned article: Introduction to the OurBigBook Project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 2. You can publish local OurBigBook lightweight markup files to either OurBigBook.com or as a static website.
Figure 3. Visual Studio Code extension installation.
Figure 5. . You can also edit articles on the Web editor without installing anything locally. Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension. 
- Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact