For IP-level communication, askubuntu.com/questions/22835/how-to-network-two-ubuntu-computers-using-ethernet-without-a-router/116680#116680 just worked between P51 and P14s both on Ubuntu 23.10 connected with a regular Cat 5e cable.
On both machines, first we found the Ethernet cable interface name with the ip CLI tool:
ip a
which outputs on the P41s:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp1s0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether fc:5c:ee:24:fb:b4 brd ff:ff:ff:ff:ff:ff
3: wlp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 04:7b:cb:cc:1b:10 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.123/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp2s0
       valid_lft 61284sec preferred_lft 61284sec
    inet6 fe80::3597:15d8:74ff:e112/64 scope link noprefixroute
       valid_lft forever preferred_lft forever
so the interface was enp1s0f0, because wlp is wireless and lo is localhost.
So on the P14s we assign an IP of 10.0.0.10 to the P51:
sudo ip address add 10.0.0.10/24 dev enp1s0f0
Then on the P51 analogously, giving IP of 10.0.0.20 to the P14s:
sudo ip address add 10.0.0.20/24 dev enp0s31f6
And after that, P14s can:
ping 10.0.0.10
and P51 can:
ping 10.0.0.20
TODO after a few seconds, the settings appear to be forgotten, and ping stops working unless you do sudo ip address add on the local machine again. This seems to happen after a popup appears saying "Activation of network connection failed" as it fails to obtain Internet from the cable.
TODO list and delete such manual assignments we've made.
The beauty of mathematics Updated 2025-07-16
Ciro Santilli intends to move his beauty list here little by little: github.com/cirosantilli/mathematics/blob/master/beauty.md
The most beautiful things in mathematics are results that are:
Good lists of such problems Lists of mathematical problems.
Whenever Ciro Santilli learns a bit of mathematics, he always wonders to himself:
Am I achieving insight, or am I just memorizing definitions?
Unfortunately, due to how man books are written, it is not really possible to reach insight without first doing a bit of memorization. The better the book, the more insight is spread out, and less you have to learn before reaching each insight.
Waring-Goldbach problem Updated 2025-07-16
It is exactly what you'd expect from the name, Waring was watching Netflix with Goldbach, when they suddenly came up with this.
Water Updated 2025-07-16
"Water" is the name for both:
Figure 2.
Ball-and-stick model of a water molecule
. Source.
Figure 3.
Simplified phase diagram of water
. Source. Note the triple point and critical point visible. Phase diagrams are so cool!
Figure 4.
Phase diagram of water
. Source. Note all the obscure phases of ice.
Game theory Updated 2025-07-16
As mentioned at Human Compatible by Stuart J. Russell (2019), game theory can be seen as the part of artificial intelligence that deas with scenarios where multiple intelligent agents are involved.
Street reclamation Updated 2025-07-16
Only people who need to drive a car should be allowed to drive a car anywhere near a city, e.g. people who work door to door, people who are disabled, etc.
Countryside driving is fine. If going to a city, you just have to drive to a parking outside of the city where you then take the public transport. And those who live in cities must leave their cars there too.
Everyone else must walk or cycle from home to public transport.
Cars just destroy everything, they make everything ugly:
  • this was extremely clear to Ciro Santilli as a cyclist. He previously lived in a place with few cars and the countryside was so pleasant. Then he moved to a place with more cars and it was shocking. It's a mixture of pollution, noise, and the fact that roads cut up the countryside that just make things not pleasant at all. Dual lane roads in particular are just a terrible thing. You can hear them from afar, much before you see them.
    You can just see as tiny little villages surrounding the bit city and it's oversized motorways are more or less homogenized into one big city mass, the process is clearly visible as you cycle out of the big city and the villages become nicer and more unique as you go along further out.
  • even within cities, cars completely dehumanize the streets. For example, Ciro once lived in a small dead end street, and he would have gladly opened his front window more often to meet the neighbours. But just the noise of cars passing by every so often makes it impractical to work like that.
The Zatoichi effect applies well to the problem of cyclists:
  • they are not really pedestrians, and pedestrian paths are not suitable to them because they are too narrow, of not smooth, or curved. But pedestrians will always have enough political power to have their paths, because they live around the paths
  • they are not really motor vehicles, because motor vehicle paths are too wide and too fast for them. But motor vehicles will always have enough political power to have their paths, because people are lazy and stupid, and because as the world stands, individually you just don't have any reasonable choice to go anywhere.
This is the main drama faced by cyclists.
Lobbying groups:
Video 1.
Why isn't cycling normal in London? by Jay Foreman (2018)
Source.
Christianism Updated 2025-07-16
Verilator Updated 2025-07-16
Verilog simulator that transpiles to C++.
One very good thing about this is that it makes it easy to create test cases directly in C++. You just supply inputs and clock the simulation directly in a C++ loop, then read outputs and assert them with assert(). And you can inspect variables by printing them or with GDB. This is infinitely more convenient than doing these IO-type tasks in Verilog itself.
Some simulation examples under verilog.
First install Verilator. On Ubuntu:
sudo apt install verilator
Tested on Verilator 4.038, Ubuntu 22.04.
Run all examples, which have assertions in them:
cd verilator
make run
File structure is for example:
Example list:
Verilator interactive example Updated 2025-07-16
The example under verilog/interactive showcases how to create a simple interactive visual Verilog example using Verilator and SDL.
https://raw.githubusercontent.com/cirosantilli/media/master/verilog-interactive.gif
You could e.g. expand such an example to create a simple (or complex) video game for example if you were insane enough. But please don't waste your time doing that, Ciro Santilli begs you.
Usage: install dependencies:
sudo apt install libsdl2-dev verilator
then run as either:
make run RUN=and2
make run RUN=move
Tested on Verilator 4.038, Ubuntu 22.04.
In those examples, the more interesting application specific logic is delegated to Verilog (e.g.: move game character on map), while boring timing and display matters can be handled by SDL and C++.
Here's to the crazy ones Updated 2025-07-16
Because the people who are crazy enough to think they can change the world are the ones who do.
Video 1.
50,000,000x Magnification by AlphaPhoenix (2022)
Source.
Subquotient Updated 2025-07-16
That normal subgroup does not have have to be a normal subgroup of G.
As an overkill example, the happy family are subquotients of the monster group, but the monster group is simple.
Suikoden Updated 2025-07-16
This game (1 or 2, can't remember) made an impression on Ciro Santilli for some reason.
Only many many years after playing it, after Ciro started getting more interested, did he learn that it was actually an adaptation of the Chinese mega-classic Water Margin.
"Suikoden" is the actual Japenese transliteration for the Chinese name of the original Water Margin novel.
The game puts great emphasis on the concept of the 108 Stars of Destiny, which never left Ciro's mind: making 108 allies, the main collectible of the game, allows you to make a more powerful alliance, and unlock better endings.

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