Ciro Santilli (@cirosantilli) - New articles

Nonprofit impact measurement  Updated 2025-03-28  +Created 1970-01-01

It is harder to measure the impact of nonprofits than of for-profits, since you can't just look at their bank balances.

This is one fundamental difficulty of nonprofit work, how to prove that you deserve the investments and not someone else.

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The best articles by Ciro Santilli  Updated 2025-03-28  +Created 1970-01-01

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These are the best articles ever authored by Ciro Santilli, most of them in the format of Stack Overflow answers.

Ciro posts update about new articles on his Twitter accounts.

A chronological list of all articles is also kept at: Section "Updates".

Some random generally less technical in-tree essays will be present at: Section "Essays by Ciro Santilli".

Trended on Hacker News:
- CIA 2010 covert communication websites on 2023-06-11. 190 points, a mild success.
- x86 Bare Metal Examples on 2019-03-19. 513 points. The third time something related to that repo trends. Hacker news people really like that repo!
  - again 2020-06-27 (archive). 200 points, repository traffic jumped from 25 daily unique visitors to 4.6k unique visitors on the day
- How to run a program without an operating system? on 2018-11-26 (archive). 394 points. Covers x86 and ARM
- ELF Hello World Tutorial on 2017-05-17 (archive). 334 points.
- x86 Paging Tutorial on 2017-03-02. Number 1 Google search result for "x86 Paging" in 2017-08. 142 points.
  Figure 1.
  BIOS bare metal hello world running on a Lenovo ThinkPad T430
  . Source.
x86 assembly
- What does "multicore" assembly language look like?
- What is the function of the push / pop instructions used on registers in x86 assembly? Going down to memory spills, register allocation and graph coloring.
Linux kernel
QEMU
gcc and Binutils:
- How do linkers and address relocation works?
- What is incremental linking or partial linking?
- GOLD (-fuse-ld=gold) linker vs the traditional GNU ld and LLVM ldd
- What is the -fPIE option for position-independent executables in GCC and ld? Concrete examples by running program through GDB twice, and an assembly hello world with absolute vs PC relative load.
- How many GCC optimization levels are there?
- Why does GCC create a shared object instead of an executable binary according to file?
C/C++: almost all of those fall into "disassemble all the things" category. Ciro also does "standards dissection" and "a new version of the standard is out" answers, but those are boring:
- What does "static" mean in a C program?
- In C++ source, what is the effect of extern "C"?
- Char array vs Char Pointer in C
- How to compile glibc from source and use it?
- When should static_cast, dynamic_cast, const_cast and reinterpret_cast be used?
- What exactly is std::atomic in C++?. This answer was originally more appropriately entitled "Let's disassemble some stuff", and got three downvotes, so Ciro changed it to a more professional title, and it started getting upvotes. People judge books by their covers.
- notmain.o 0000000000000000 0000000000000017 W MyTemplate<int>::f(int) main.o 0000000000000000 0000000000000017 W MyTemplate<int>::f(int)
  Code 1.
  nm outputs showing that objects are redefined multiple times across files if you don't use template instantiation properly
  . From: What is explicit template instantiation in C++ and when to use it?

IEEE 754

What is difference between quiet NaN and signaling NaN?
In Java, what does NaN mean?

Without subnormals:

          +---+---+-------+---------------+-------------------------------+
exponent  | ? | 0 |   1   |       2       |               3               |
          +---+---+-------+---------------+-------------------------------+
          |   |   |       |               |                               |
          v   v   v       v               v                               v
          -----------------------------------------------------------------
floats    *    **** * * * *   *   *   *   *       *       *       *       *
          -----------------------------------------------------------------
          ^   ^   ^       ^               ^                               ^
          |   |   |       |               |                               |
          0   |   2^-126  2^-125          2^-124                          2^-123
              |
              2^-127

With subnormals:

          +-------+-------+---------------+-------------------------------+
exponent  |   0   |   1   |       2       |               3               |
          +-------+-------+---------------+-------------------------------+
          |       |       |               |                               |
          v       v       v               v                               v
          -----------------------------------------------------------------
floats    * * * * * * * * *   *   *   *   *       *       *       *       *
          -----------------------------------------------------------------
          ^   ^   ^       ^               ^                               ^
          |   |   |       |               |                               |
          0   |   2^-126  2^-125          2^-124                          2^-123
              |
              2^-127

Code 2.

Visualization of subnormal floating point numbers vs what IEEE 754 would look like without them

. From: What is a subnormal floating point number?

Computer science
- Algorithms
  - Figure 5.
    Average insertion time into heaps, binary search tree and hash maps of the C++ standard library
    . Source. From: Heap vs Binary Search Tree (BST)
- Is it necessary for NP problems to be decision problems?
- Polynomial time and exponential time. Answered focusing on the definition of "exponential time".
- What is the smallest Turing machine where it is unknown if it halts or not?. Answer focusing on "blank tape" initial condition only. Large parts of it are summarizing the Busy Beaver Challenge, but some additions were made.

Git

  | 0           | 4            | 8           | C              |
  |-------------|--------------|-------------|----------------|
0 | DIRC        | Version      | File count  | ctime       ...| 0
  | ...         | mtime                      | device         |
2 | inode       | mode         | UID         | GID            | 2
  | File size   | Entry SHA-1                              ...|
4 | ...                        | Flags       | Index SHA-1 ...| 4
  | ...                                                       |

Code 3.

ASCII art depicting the binary file format of the Git index file

. From: What does the git index contain EXACTLY?

tree {tree_sha}
{parents}
author {author_name} <{author_email}> {author_date_seconds} {author_date_timezone}
committer {committer_name} <{committer_email}> {committer_date_seconds} {committer_date_timezone}

{commit message}

Code 4.

Description of the Git commit object binary data structure

. From: What is the file format of a git commit object data structure?

How do I clone a subdirectory only of a Git repository?

Python
- What is the difference between old style and new style classes in Python?
- What is a mixin in Python, and why are they useful?
- What are the differences between threads and processes in Python?
  Figure 6.
  Python Threads vs Processes with 8 hyperthreads
  . Source.
Web technology
- What does enctype='multipart/form-data' mean?
- JavaScript
  - How does JavaScript .prototype work?
  - What is the difference between .prop() vs .attr() in JavaScript?
OpenGL
- Figure 7.
  OpenGL rendering output dumped to a GIF file
  . Source. From: How to use GLUT/OpenGL to render to a file?
- Figure 8.
  Example of a texture atlas containing glyphs
  . Source.
  Image by Nicolas P. Rougier, author of Freetype GL.
  Used on Ciro Santilli's answer: How to draw text using only OpenGL methods?
- Figure 9.
  OpenGL glFrustrum vs glOrtho
  . Source. From: How to use glOrtho() in OpenGL?
- What are shaders in OpenGL?
- Why do we use 4x4 matrices to transform things in 3D?
- Figure 10.
  Sinusoidal circular wave heatmap generated with an OpenGL shader at 60 FPS on SDL
  . Source.
  From: Is it possible to build a heatmap from point data at 60 times per second?
  Compared CPU vs GPU shaders.
- Image Processing with GLSL shaders? Compared the CPU and GPU for a simple blur algorithm.
  Figure 11. Source.
  Video 1.
  OpenGL GPU GLSL fragment shader real time v4l2 Linux webcam computer vision box blur vs CPU
  . Source.
Node.js
- What's the difference between dependencies, devDependencies and peerDependencies in npm package.json file?
Ruby on Rails
- What is the difference between +<%+, +<%=+, +<%#+ and +-%>+ in ERB in Rails?
POSIX
- What is POSIX? Huge classified overview of the most important things that POSIX specifies.

Systems programming

What do the terms "CPU bound" and "I/O bound" mean?
Figure 12.
Plot of "real", "user" and "sys" mean times of the output of time for CPU-bound workload with 8 threads
. Source. From: What do 'real', 'user' and 'sys' mean in the output of time?

+--------+                  +------------+       +------+
| device |>---------------->| function 0 |>----->| BAR0 |
|        |                  |            |       +------+
|        |>------------+    |            |
|        |             |    |            |       +------+
   ...        ...      |    |            |>----->| BAR1 |
|        |             |    |            |       +------+
|        |>--------+   |    |            |
+--------+         |   |         ...        ...    ...
                   |   |    |            |
                   |   |    |            |       +------+
                   |   |    |            |>----->| BAR5 |
                   |   |    +------------+       +------+
                   |   |
                   |   |
                   |   |    +------------+       +------+
                   |   +--->| function 1 |>----->| BAR0 |
                   |        |            |       +------+
                   |        |            |
                   |        |            |       +------+
                   |        |            |>----->| BAR1 |
                   |        |            |       +------+
                   |        |            |
                   |             ...        ...    ...
                   |        |            |
                   |        |            |       +------+
                   |        |            |>----->| BAR5 |
                   |        +------------+       +------+
                   |
                   |
                   |             ...
                   |
                   |
                   |        +------------+       +------+
                   +------->| function 7 |>----->| BAR0 |
                            |            |       +------+
                            |            |
                            |            |       +------+
                            |            |>----->| BAR1 |
                            |            |       +------+
                            |            |
                                 ...        ...    ...
                            |            |
                            |            |       +------+
                            |            |>----->| BAR5 |
                            +------------+       +------+

Code 5.

Logical struture PCIe device, functions and BARs

. From: What is the Base Address Register (BAR) in PCIe?

Electronics
- Raspberry Pi
  - Figure 13.
    Raspberry Pi 2 directly connected to a laptop with an Ethernet cable
    . Image from answer to: How to hook up a Raspberry Pi via Ethernet to a laptop without a router?
    Figure 14.
    Raspberry Pi 2 connected to a laptop with an USB UART adapter
    . Image from answer to: How to hook up a Raspberry Pi via Ethernet to a laptop without a router?
    Figure 15.
    Raspberry Pi OS being emulated on QEMU 2.5.0 on Ubuntu 16.04 with a modified kernel
    . Image from answer to: How to emulate the Raspberry Pi 2 on QEMU?
    Figure 16.
    Bare metal LED blinker program running on a Raspberry Pi 2
    . Image from answer to: How to run a C program with no OS on the Raspberry Pi?
Computer security
- Why is the same origin policy so important?
Media
- Video 2.
  Canon in D in C
  . Source.
  From: How is audio represented with numbers in computers?.
  The original question was deleted, lol...: How to programmatically synthesize music?
- How to resize a picture using ffmpeg's sws_scale()?
- Is there any decent speech recognition software for Linux? ran a few examples manually on vosk-api and compared to ground truth.
Eclipse
- How to set up the Eclipse for remote C debugging with gdbserver?
Computer hardware
- Are there good open source standard cell libraries to learn IC synthesis with EDA tools?
Scientific visualization software
- Figure 17.
  VisIt zoom in 10 million straight line plot with some manually marked points
  . Source. From: Section "Survey of open source interactive plotting software with a 10 million point scatter plot benchmark by Ciro Santilli"
Numerical analysis
- Video 3.
  Real-time heat equation OpenGL visualization with interactive mouse cursor using relaxation method by Ciro Santilli (2016)
  Source.
Computational physics
- Figure 18.
  gnuplot plot of the y position of a sphere bouncing on a plane simulated in Bullet Physics
  . Source. From: What is the simplest collision example possible in a Bullet Physics simulation?
Register transfer level languages like Verilog and VHDL
- Verilog:
  Figure 19.
  Interacgive ASDF-controlled demo with core logic written in Verilog using Verilator
  .
  From: Is it possible to do interactive user input and output simulation in VHDL or Verilog?
  See also: Section "Verilator interactive example"
Android
- Figure 20. Source. From: How to compile the Android AOSP kernel and test it with the Android Emulator?
- Video 4.
  Android screen showing live on an Ubuntu laptop through ADB
  . Source. From: How to see the Android screen live on an Ubuntu desktop through ADB?
Debugging
Program optimization
- What is tail call optimization?
- Figure 21.
  gprof2dot image generated from the gprof data of a simple test program
  . Source.
  From: How can I profile C++ code running on Linux?
  The answer compares gprof, valgrind callgrind, perf and gperftools on a single simple executable.
Data
- Figure 22.
  Mathematics dump of Wikipedia CatTree
  . Source. In this project, Ciro Santilli explored extracting the category and article tree out of the Wikipedia dumps.
Mathematics
- Figure 23.
  Diagram of the fundamental theorem on homomorphisms by Ciro Santilli (2020)
  
  Shows the relationship between group homomorphisms and normal subgroups.
  From: What is the intuition behind normal subgroups?
- Section "Formalization of mathematics": some early thoughts that could be expanded. Ciro almost had a stroke when he understood this stuff in his teens.
- Figure 24.
  Simple example of the Discrete Fourier transform
  . Source. That was missing from Wikipedia page: en.wikipedia.org/wiki/Discrete_Fourier_transform!
Network programming
- How to make an HTTP get request in C without libcurl?
Physics
- What is the difference between plutonium and uranium?
- Figure 25.
  Spacetime diagram illustrating how faster-than-light travel implies time travel
  . From: Does faster than light travel imply travelling back in time?
Biology
- Figure 26.
  Top view of an open Oxford Nanopore MinION
  . Source. From: Section "How to use an Oxford Nanopore MinION to extract DNA from river water and determine which bacteria live in it"
- Figure 27.
  Mass fractions in a minimal growth medium vs an amino acid cut in a simulation of the E. Coli Whole Cell Model by Covert Lab
  . Source. From: Section "E. Coli Whole Cell Model by Covert Lab"
Quantum computing
- Section "Quantum computing is just matrix multiplication"
- Figure 28.
  Visualization of the continuous deformation of states as we walk around the Bloch sphere represented as photon polarization arrows
  . From: Understanding the Bloch sphere.
Bitcoin
- Section "Cool data embedded in the Bitcoin blockchain"
GIMP
- Figure 29.
  GIMP screenshot part of how to combine two images side-by-side in GIMP?
  .
Home DIY
- Figure 30.
  Total_Blackout_Cassette_Roller_Blind_With_Curtains.
  Source. From: Section "How to blackout your window without drilling"
China
- What would happen if I walked around Beijing with a t-shirt that said "freedom of speech is pretty great"?

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Microwave  Updated 2025-03-28  +Created 1970-01-01

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Micro means "small wavelength compared to radio waves", not micron-sized.

Microwave production and detection is incredibly important in many modern applications:

telecommunications, e.g. being used in
- Wi-Fi
- satellite communications
  youtu.be/EYovBJR6l5U?list=PL-_93BVApb58SXL-BCv4rVHL-8GuC2WGb&t=27 from CuriousMarc comments on some piece of Apollo equipment they were restoring/reversing:
  These are the boxes that brought you voice, data and live TV from the moon, and should be early masterpieces of microwave electronics, the blackest of black arts in analog electronics.
  Ah, Ciro Santilli really wishes he knew what that meant more precisely. Sounds so cool!
- 4G and other cellular network standards
radar. As an example, 1965 Nobel Prize in Physics laureate Julian Schwinger did some notable work in the area in World War II, while most other physicists went to the Manhattan Project instead.
This is well highlighted in QED and the men who made itby Silvan Schweber (1994). Designing the cavity wasn't easy. One of the key initial experiments of quantum electrodynamics, the Lamb-Retherford experiment from 1947, fundamental for modern physics, was a direct consequence of post-radar research by physicists who started to apply wartime developments to their scientific search.
Wikipedia also mentions en.wikipedia.org/w/index.php?title=Microwave&oldid=1093188913#Radar_2:
The first modern silicon and germanium diodes were developed as microwave detectors in the 1930s, and the principles of semiconductor physics learned during their development led to semiconductor electronics after the war.
microwave is the natural frequency of several important Atomic, Molecular and Optical Physics phenomena, and has been used extensively in quantum computing applications, including completely different types of quantum computer type:
- trapped ion quantum computer; Video "Trapping Ions for Quantum Computing by Diana Craik (2019)"
- superconducting quantum computer; e.g. this Junior Microwave Design Engineer job accouncement from Alice&Bob: archive.ph/wip/4wGPJ
Likely part of the appeal of microwaves is that they are non-ionizing, so you don't destroy stuff. But at the same time, they are much more compatible with atomic scale energies than radio waves, which have way way too little energy.

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Accounts controlled by Ciro Santilli  Updated 2025-03-28  +Created 1970-01-01

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Ciro Santilli controls the following accounts.

With non-trivial activity:

github.com/cirosantilli on GitHub
stackoverflow.com/users/895245 on Stack Overflow
www.linkedin.com/in/cirosantilli on LinkedIn
www.youtube.com/c/CiroSantilli on YouTube
Twitter: see Section "Ciro Santilli's Twitter accounts"
archive.org/details/@cirosantilli2 on the Internet Archive. Was archive.org/details/@cirosantilli but got deleted due to an "admin error" and the old username cannot be restored!^[ref]
en.wikipedia.org/wiki/User:Cirosantilli2 and commons.wikimedia.org/wiki/User:Cirosantilli2: Ciro tries to upload all educational CC content he creates to Wikimedia Commons as an extra backup and sometimes to use in Wikipedia pages
www.facebook.com/cirosantilli/ Ciro accepts all friend requests there, but expect a few non-technical posts. Unless you look like a massive honeypot account, please send context in advance in that case.
www.quora.com/profile/Ciro-Santilli
www.reddit.com/user/cirosantilli/ is Ciro's Reddit account, mostly computer and China topics
maps.app.goo.gl/npV35XTppSBTmNqC8: Google Maps. Ciro Santilli likes to make additions to certain niche topics that are missing, having reached Local Guide Level 6 as of 2024. He can't do as much as he'd like so as to not reveal his current city however.

Trivial or no activity:

Profiles without URLs (OMG...):

Discord: username cirosantilli, previously cirosantilli#8921

Accounts in Chinese websites. These accounts might be banned or altered or offer other limitations, so Ciro only communicates briefly through them. All communication through those channels should obviously be assumed to be compromised:

bbs.nibaedu.com/index.php?m=space&uid=70
www.renren.com/338003848/profile
www.tianya.cn/109285544 (can't post, no cell phone)
hacpai.com/member/cirosantilli unable to login as of 2019-10-12, reason unclear, either ban or website too crappy.
pincong.rocks/people/cirosantilli Lost account tested as of 2022-11 and likely much earlier. Last existing password not working, and there doesn't seem to be a reset password button. Creating cirosantilli2
pincong.rocks/people/cirosantilli2
tieba.baidu.com/home/main?id=5cd56369726f73616e74696c6c69c944
v2ex.com/member/cirosantilli: Ciro was blocked and or account deleted on 2020-07-23: cirosantilli.com/china-dictatorship/v2ex
- v2ex.com/member/cirosantilli2: was created by someone else most likely and cannot be re-registered. Also blocked.
- v2ex.com/member/cirosantilli3: Ciro created this new account November 2023, let's see how long it lasts.
www.zhihu.com/people/cirosantilli. Ciro was prevented from posting in 2018-06-25, and the account and all content mentioning him were taken down in 2019-11-03.
www.weibo.com/p/1005055601627311: started requiring a cell phone to login in 2020, and Ciro didn't want to give his cell phone number to the CCP and didn't have the patience to manage a secondary phone number, so he is not logging in for now. The account was blocked in 2021: cirosantilli.com/china-dictatorship/ciro-santillis-weibo-block

Accounts in Russian websites:

vk.com/id595305194

Dead websites:

www.citeulike.org/user/cirosantilli (2019-05)

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Military-industrial complex  Updated 2025-03-28  +Created 1970-01-01

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This is notably what the United States emerged to be after World War II. But it was likely what Nazi Germany also was, and many other superpowers.

Ciro Santilli feels that much more relevant would be to also include academia as in "military-industrial-academic" complex, the Wikipedia page actually mentions precedents to this idea.

The addition of congress/politicians is also relevant.

But hey, the name wouldn't sound so slick with three parts.

It is basically in this context that American science and technology flourished after World War II, including notably the development of quantum electrodynamics, Richard Feynman being a prototypical example, having previously worked on the Manhattan Project.

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The next big thing  Updated 2025-03-28  +Created 1970-01-01

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If you are going to live, you might as well chase one of them.

You might not achieve them in your lifetime, but you never know. At some point, the pieces just "fall into place", and they happen.

And they will all come from deep tech.

Ciro Santilli would like to contribute to them. but this is a bit less realistic than software projects.

But who knows? Maybe he can code some stuff in those areas.

And one can at least have some fun by learning deeply about those subjects.

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ImageMagick HOWTO  Updated 2025-03-28  +Created 1970-01-01

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Calculus of variations  Updated 2025-03-28  +Created 1970-01-01

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Calculus of variations is the field that searches for maxima and minima of Functionals, rather than the more elementary case of functions from

R

to

R

.

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Induced pluripotent stem cell  Updated 2025-03-28  +Created 1970-01-01

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Heavyside step function  Updated 2025-03-28  +Created 1970-01-01

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University of California, Santa Barbara  Updated 2025-03-28  +Created 1970-01-01

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The third one of the University of California after UC Berkeley and UCLA.

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UPDATE with JOIN (SQL)  Updated 2025-03-28  +Created 1970-01-01

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Dumping examples under nodejs/sequelize/raw/many_to_many.js.

Not possible without subqueries in the standard syntax, a huge shame: stackoverflow.com/questions/1293330/how-can-i-do-an-update-statement-with-join-in-sql-server

The UPDATE + FROM extension exists in a few DBMSs:

ORM:

Sequelize: UPDATE with JOIN in Sequelize

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Minetest  Updated 2025-03-28  +Created 1970-01-01

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github.com/minetest/minetest Written in C++, which is, a plus.

Good Minecraft clone. On Ubuntu 21.10 did:

sudo snap install minetest

which installed 5.4.1, and it worked, except it had no sound, to an error:

ERROR[Main]: Audio: Global Initialization: Failed to open device

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STED microscopy  Updated 2025-03-28  +Created 1970-01-01

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Stefan Hell was really excited by this as of 2023.

Instead of shining a light over the entire sample to saturate it, you illuminate just a small bit instead.

He was basically saying that this truly brings the resolution to the actual physical limits, going much much beyond 2014 Nobel prize levels.

Figure 1.
Illumination patterns for STED microscopy
. Source.

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5S ribosomal RNA  Updated 2025-03-28  +Created 1970-01-01

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Nokia G22 (2023)  Updated 2025-03-28  +Created 1970-01-01

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£112.99

Buying October 2023 as an immediate backup phone after the Google Pixel 3a (2020) touchscreen died, and Motorola Moto G6 Play (2018) wouldn't connect to giffgaff.

www.gsmarena.com/nokia_g22-12137.php

Still working checks: May 2024.

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Gas hob  Updated 2025-03-28  +Created 1970-01-01

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SMEG, cannot determine exact model.

2020-11: started sparking by itself once every 5 minutes. Knob controls dirty in hole, but can't find out how to access. Seems slightly glued insulated around edges.

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Archaea are more cosely related to the eukaryotes than bacteria  Updated 2025-03-28  +Created 1970-01-01

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Arbitrary code execution  Updated 2025-03-28  +Created 1970-01-01

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Training, validation, and test data sets  Updated 2025-03-28  +Created 1970-01-01

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stats.stackexchange.com/questions/19048/what-is-the-difference-between-test-set-and-validation-set

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Ciro Santilli @cirosantilli 35