Ciro Santilli @cirosantilli 37

Skew-symmetric bilinear map that is also a bilinear form.

How to build it: math.stackexchange.com/questions/3137319/how-in-general-does-one-construct-a-cycle-graph-for-a-group/3162746#3162746 good answer with ASCII art. You basically just pick each element, and repeatedly apply it, and remove any path that has a longer version.

Immediately gives the generating set of a group by looking at elements adjacent to the origin, and more generally the order of each element.

TODO uniqueness: can two different groups have the same cycle graph? It does not seem to tell us how every element interact with every other element, only with itself. This is in contrast with the Cayley graph, which more accurately describes group structure (but does not give the order of elements as directly), so feels like it won't be unique.

A concise to describe a specific permutation.

A permutation group can then be described in terms of the generating set of a group of specific elements given in cycle notation.

E.g. en.wikipedia.org/w/index.php?title=Mathieu_group&oldid=1034060469#Permutation_groups mentions that the Mathieu group $M_{11}$ is generated by three elements:which feels quite compact for a simple group with 95040 elements, doesn't it!

One of the most powerful chess engine as of 2023: computer chess competition.

CLI program implementing Universal Chess Interface: www.reddit.com/r/ComputerChess/comments/b6rdez/commandline_options_for_stockfish/

How to actually play against it: chess.stackexchange.com/questions/4353/how-to-install-stockfish-on-ubuntu So hard!

Bibliography: discuss.bbchallenge.org/t/decider-cyclers/33

Example: bbchallenge.org/279081.

These are very simple, they just check for exact state repetitions, which obviously imply that they will run forever.

Unfortunately, cyclers may need to run through an initial setup phase before reaching the initial cycle point, which is not very elegant.

Also, we have no way of knowing the initial setup length of the actual cycle length, so we just need an arbitrary cutoff value.

And unfortunately, this can lead to misses, e.g. Skelet machine #1, a 5 state machine, has a (translated) cycle that starts at around 50-200M steps, and takes 8 trillion steps to repeat.

I caught and overcame a minor addiction to Cataclysm: Dark Days Ahead.

It does bring back the The Sims feeling from my teenage years, but with killer zombies added in.

I especially like going to sleep in that game, and how you need to setup a confy bed for it.

Some further comments at: Section "Cataclysm: Dark Days Ahead".

The way to quit is simple: delete your saves, then get annoyed with slowness of progressing back up, then use built-in debug/cheat menu to overcome that, then it's not fun anymore. This is a major advantage of single player open source games: addiction resistance!

Added font awesome icons. github.com/ourbigbook/ourbigbook/issues/151

Didn't manage to subset, but so be it for now: stackoverflow.com/questions/62395038/how-can-i-export-only-one-character-from-ttf-woff-file-to-avoid-load-unnecessa/71197892#71197892

TODO understand.

After something broke on the website due to SQLite vs PostgreSQL inconsistencies and took me a day to figure it out, I finally decided to update the test system so that OURBIGBOOK_POSTGRES=true npm test will run the tests on PostgreSQL.

Originally, these were being run only on SQLite, which is the major use case for OurBigBook CLI, which came before the website.

But the website runs on PostgreSQL, so it is fundamental to test things in PostgreSQL as well.

We know that superfluidity happens more easily in bosons, and so electrons joins in Cooper pairs to form bosons, making a superfluid of Cooper pairs!

Isn't that awesome!

For each process, the virtual address space looks like this:

The kernel maintains a list of pages that belong to each process, and synchronizes that with the paging.

If the program accesses memory that does not belong to it, the kernel handles a page-fault, and decides what to do:

When an ELF file is loaded by the kernel to start a program with the exec system call, the kernel automatically registers text, data, BSS and stack for the program.

The brk and mmap areas can be modified by request of the program through the brk and mmap system calls. But the kernel can also deny the program those areas if there is not enough memory.

brk and mmap can be used to implement malloc, or the so called "heap".

mmap is also used to load dynamically loaded libraries into the program's memory so that it can access and run it.

Stack allocation: stackoverflow.com/questions/17671423/stack-allocation-for-process

Calculating exact addresses Things are complicated by:

Why the text does not start at 0: stackoverflow.com/questions/14795164/why-do-linux-program-text-sections-start-at-0x0804800-and-stack-tops-start-at-0

Minimal example: github.com/cirosantilli/x86-bare-metal-examples/blob/5c672f73884a487414b3e21bd9e579c67cd77621/paging.S

Like everything else in programming, the only way to really understand this is to play with minimal examples.

What makes this a "hard" subject is that the minimal example is large because you need to make your own small OS.

The United Kingdom is a great place to cycle in general as there's plenty of small country roads and interesting new small towns to discover, perhaps much like the rest of Europe, as opposed to the United States, which likely has some huge infinitely long straight roads with a lot of nothing in between.

Of particular interest is the large amount of airfields and small air raid shelters in the fields, an ominous reminder of world war 2. The airfields are in various states, from functional military fields, many converted to civilian usage, some have barely any tarmac left but still see usage. And some were just completely abandoned and decayed and became recreation grounds and farms. The UK is therefore also a great place to be if you want to learn to fly as a hobby!

Good starting point:

Next, you want to decide about nice destinations to reach/go through, and these are good ideas to look into: