Ciro Santilli @cirosantilli 37

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Peptidoglycan Updated 2025-07-16

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Forms the bacterial cell wall.

From the Wikipedia image we can see clearly the polymer structure formed: it is a mesh with:

sugar covalent bond chains in one direction. These have two types of monosaccharide, NAM and NAG
peptide chains on the other, and only coming off from NAM

Figure 1.
Peptidoglycan polymer structure
. Source.

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Pernosco Updated 2025-07-16

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pernos.co/

Proprietary extension to Mozilla rr by rr lead coder Robert O'Callahan et. al, started in 2016 after he quit Mozilla.

TODO what does it add to rr?

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Physics Letters A Updated 2025-07-16

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www.sciencedirect.com/journal/physics-letters-a

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Physics research institute Updated 2025-07-16

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Pinto bean Updated 2025-07-16

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This seems to be the "brown Brazilian bean" that many Brazilians eat every day.

Edit: after buying it, not 100% sure. This one felt smaller than what Ciro had in Brazil, borlotti beans might be closer. Pinto beans are smaller, and creamier, and have softer peel, possibly produced less natural gas.

2021-04: second try.

2021-03: did for first time, started with same procedure as borlotti beans 2021-03. Maybe 1h30 is too much. Outcome was still very good.

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Pipa piece Updated 2025-07-16

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TODO identify better:

Video 1.

Posing As a Wind Instrument Player In an Ensemble by Li Xuan

. Source. Part of "Chinese Ancient Music - Vol 2, High Mountains And Flowing Water", e.g. as seen at: www.youtube.com/watch?v=If7ARKoMiKI.

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Plancherel theorem Updated 2025-07-16

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Some sources say that this is just the part that says that the norm of a

L^{2}

function is the same as the norm of its Fourier transform.

Others say that this theorem actually says that the Fourier transform is bijective.

The comment at math.stackexchange.com/questions/446870/bijectiveness-injectiveness-and-surjectiveness-of-fourier-transformation-define/1235725#1235725 may be of interest, it says that the bijection statement is an easy consequence from the norm one, thus the confusion.

TODO does it require it to be in

L^{1}

as well? Wikipedia en.wikipedia.org/w/index.php?title=Plancherel_theorem&oldid=987110841 says yes, but courses.maths.ox.ac.uk/node/view_material/53981 does not mention it.

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PlanetMath Updated 2025-07-16

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planetmath.org/

Based on GitHub pull requests: github.com/planetmath

Joe Corneli, of of the contributors, mentions this in a cool-sounding "Peeragogy" context at metameso.org/~joe/:

I earned my doctorate at The Open University in Milton Keynes, with a thesis focused on peer produced support for peer learning in the mathematics domain. The main case study was planetmath.org; the ideas also informed the development of “Peeragogy”.

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Plausible deniability of email password handover Updated 2025-07-16

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protonmail.uservoice.com/forums/284483-feedback/suggestions/39962275-plausible-deniability

You need a secondary password that when used leads to an empty inbox with a setting set where message are deleted after 2 days.

This way, if the attacker sends a test email, it will still show up, but being empty is also plausible.

Of course, this means that any new emails received will be visible by the attacker, so you have to find a way to inform senders that the account has been compromised.

So you have to find a way to inform senders that the account has been compromised, e.g. a secret pre-agreed canary that must be checked each time as part of the contact protocol.

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Plutonium Updated 2025-07-16

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Vs uranium: uranium vs plutonium Quora answer by Ciro Santilli.

What a material:

only exists in trace amounts in nature,but it can be produced at kilogram scale in breeder reactors
it is only intentionally produced for one application, and one application only basically: nuclear weapons

Video 1. Source. Plutonium for self-respect scene from the 1987 film Edge of Darkness

Video 2.

Burning and Extinguishing Characteristics of Plutonium Metal Fires by RobPlonski

. Source. Commented by this dude: www.linkedin.com/in/robplonski/

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Pokemon Updated 2025-07-16

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One of the main children cartoons Ciro Santilli liked to watch. Part of the Pokemon Mania of the 90s of course.

Ciro could not understand why Nintendo won't make a proper 3D MMORPG Pokemon with actually 3D Pokemon roaming the land, which is obviously what everyone wants. There are even fan games getting there!

pokemon-mmo-3d.com Interesting concept here, where when you deploy a Pokemon, you start controlling the Pokemon rather than the main character
www.quora.com/Why-won-t-Nintendo-make-an-open-world-3D-Pokémon-RPG/answer/Ciro-Santilli

until this explaiend it beautifully Video 1. "The Downfall Of Mainline Pokemon Games by GONZ media (2020)":

Pokemon became an industrialized yearly game spitting machine, and therefore any new feature is just extra risk
Pokemon was kept mostly as a handheld exclusive to sell handlhelds, with a few early exceptions such as Pokemon Snap

Figure 1.
Instead of risking anything new, let's play it safe by continuing our slow decline into obsolecense cartoon by Tom Fishburne
. Source.

Video 1.

The Downfall Of Mainline Pokemon Games by GONZ media (2020)

Source. Great video, explains things Ciro had never thought about, e.g. how the Nintendo Switch unified handheld and console for Nintento, this could open the doors for a more ambitious Pokemon release.

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Post-quantum cryptography Updated 2025-07-16

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Encryption algorithms that run on classical computers that are expected to be resistant to quantum computers.

This is notably not the case of the dominant 2020 algorithms, RSA and elliptic curve cryptography, which are provably broken by Grover's algorithm.

However, as of 2020, we don't have any proof that any symmetric or public key algorithm is quantum resistant.

Post-quantum cryptography is the very first quantum computing thing at which people have to put money into.

The reason is that attackers would be able to store captured ciphertext, and then retroactively break them once and if quantum computing power becomes available in the future.

There isn't a shade of a doubt that intelligence agencies are actively doing this as of 2020. They must have a database of how interesting a given source is, and then store as much as they can given some ammount of storage budget they have available.

A good way to explain this to quantum computing skeptics is to ask them:

If I told you there is a 5% chance that I will be able to decrypt everything you write online starting today in 10 years. Would you give me a dollar to reduce that chance to 0.5%?

Post-quantum cryptography is simply not a choice. It must be done now. Even if the risk is low, the cost would be way too great.

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Power, performance and area Updated 2025-07-16

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en.wikichip.org/wiki/power-performance-area

This is the mantra of the semiconductor industry:

power and area are the main limiting factors of chips, i.e., your budget:
- chip area is ultra expensive because there are sporadic errors in the fabrication process, and each error in any part of the chip can potentially break the entire chip. Although there are
  The percentage of working chips is called the yield.
  In some cases however, e.g. if the error only affects single CPU of a multi-core CPU, then they actually deactivate the broken CPU after testing, and sell the worse CPU cheaper with a clear branding of that: this is called binning www.tomshardware.com/uk/reviews/glossary-binning-definition,5892.html
- power is a major semiconductor limit as of 2010's and onwards. If everything turns on at once, the chip would burn. Designs have to account for that.
performance is the goal.
Conceptually, this is basically a set of algorithms that you want your hardware to solve, each one with a respective weight of importance.
Serial performance is fundamentally limited by the longest path that electrons have to travel in a given clock cycle.
The way to work around it is to create pipelines, splitting up single operations into multiple smaller operations, and storing intermediate results in memories.

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PQShield Updated 2025-09-17

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They seem to be doing hardware acceleration for post-quantum cryptography algorithm.

One has to feel bad for them as they likely threw out entire chip designs over NIST Post-Quantum Cryptography Standardization algorithm breakeges.

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Pre-trained computer vision model Updated 2025-07-16

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Primality test Updated 2025-07-16

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Primer (YouTube channel) Updated 2025-07-16

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This channel contains several 2D continuous simulations and explains AI techniques used.

The engine appears to be open source: github.com/Primer-Learning/PrimerTools (previously at: github.com/Helpsypoo/primer). Models are closed source however.

They have several interesting multiagent game ideas.

Claims Unity-based, so has the downside of relying on a non-FOSS engine.

Ciro became mildly jealous of this channel when he found out about it, because at 800k subscribers at the time, the creator is likely able to make a living off of it, something which Ciro thought impossible.

As of 2022 he was at 1.6M followers with only 17 videos! Of course, much of those videos is about the software and they require infinite development hours to video time ratios.

Much of this success hinges a large part on the amazing 3D game presentation.

Well done!

Created by Justin Helps. Awesome name.

To make things better, the generically named channel is also the title of one of the best films of al time: Primer (2004).

Video 1.

Simulating Foraging Decisions by Primer (2020)

Source.

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Probable observation of the Josephson superconducting tunneling effect Updated 2025-07-16

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Paper by Philip W. Anderson and John M. Rowell that first (?) experimentally observed the Josephson effect.

Paywalled by the American Physical Society as of 2023 at: journals.aps.org/prl/abstract/10.1103/PhysRevLett.10.230

DOI: doi.org/10.1103/PhysRevLett.10.230

TODO understand the graphs in detail.

They used tin-oxide-lead tunnel at 1.5 K. TODO oxide of what? Why two different metals? They say that both films are 200 nm thick, so maybe it is:

   -----+------+------+-----
...  Sn | SnO2 | PbO2 | Pb  ...
   -----+------+------------
          100nm 100nm

A reconstruction of their circuit in Ciro's ASCII art circuit diagram notation TODO:

DC---R_10---X---G

There are not details of the physical construction of course. Reproducibility lol.

Figure 1.
Figure 1 of Probable observation of the Josephson superconducting tunneling effect
. TODO what do the dotted lines mean?

Figure 2.
Figure 2 of Probable observation of the Josephson superconducting tunneling effect
.

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Product definition of the exponential function Updated 2025-07-16

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e^{x} = lim_{n \to \infty} (1 + \frac{x}{n})^{n}

(1)

The basic intuition for this is to start from the origin and make small changes to the function based on its known derivative at the origin.

More precisely, we know that for any base b, exponentiation satisfies:

$b^{x + y} = b^{x} b^{y}$ .
$b^{0} = 1$ .

And we also know that for

b = e

in particular that we satisfy the exponential function differential equation and so:

\frac{d e ^{x}}{d x} (0) = 1

(2)

One interesting fact is that the only thing we use from the exponential function differential equation is the value around

x = 0

, which is quite little information! This idea is basically what is behind the importance of the ralationship between Lie group-Lie algebra correspondence via the exponential map. In the more general settings of groups and manifolds, restricting ourselves to be near the origin is a huge advantage.

Now suppose that we want to calculate

e^{1}

. The idea is to start from

e^{0}

and then then to use the first order of the Taylor series to extend the known value of

e^{0}

e^{1}

E.g., if we split into 2 parts, we know that:

e^{1} = e^{1/2} e^{1/2}

(3)

or in three parts:

e^{1} = e^{1/3} e^{1/3} e^{1/3}

(4)

so we can just use arbitrarily many parts

e^{1/ n}

that are arbitrarily close to

x = 0

e^{1} = (e^{1/ n})^{n}

(5)

and more generally for any

x

we have:

e^{x} = (e^{x / n})^{n}

(6)

Let's see what happens with the Taylor series. We have near

y = 0

in little-o notation:

e^{y} = 1 + y + o (y)

(7)

Therefore, for

y = x / n

, which is near

y = 0

for any fixed

x

e^{x / n} = 1 + x / n + o (1/ n)

(8)

and therefore:

e^{x} = (e^{x / n})^{n} = (1 + x / n + o (1/ n))^{n}

(9)

which is basically the formula tha we wanted. We just have to convince ourselves that at

lim_{n \to \infty}

, the

o (1/ n)

disappears, i.e.:

(1 + x / n + o (1/ n))^{n} = (1 + x / n)^{n}

(10)

To do that, let's multiply

e^{y}

by itself once:

e^{y} e^{y} = (1 + y + o (y)) (1 + y + o (y)) = 1 + 2 y + o (y)

(11)

and multiplying a third time:

e^{y} e^{y} e^{y} = (1 + 2 y + o (y)) (1 + y + o (y)) = 1 + 3 y + o (y)

(12)

TODO conclude.

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Program Raspberry Pi Pico W with C Updated 2025-07-26

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Ubuntu 22.04 build just worked, nice! Much feels much cleaner than the Micro Bit C setup:

sudo apt install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi libstdc++-arm-none-eabi-newlib

git clone https://github.com/raspberrypi/pico-sdk
cd pico-sdk
git checkout 2e6142b15b8a75c1227dd3edbe839193b2bf9041
cd ..

git clone https://github.com/raspberrypi/pico-examples
cd pico-examples
git checkout a7ad17156bf60842ee55c8f86cd39e9cd7427c1d
cd ..

export PICO_SDK_PATH="$(pwd)/pico-sdk"
cd pico-exampes
mkdir build
cd build
# Board selection.
# https://www.raspberrypi.com/documentation/microcontrollers/c_sdk.html also says you can give wifi ID and password here for W.
cmake -DPICO_BOARD=pico_w ..
make -j

Then we install the programs just like any other UF2 but plugging it in with BOOTSEL pressed and copying the UF2 over, e.g.:

cp pico_w/blink/picow_blink.uf2 /media/$USER/RPI-RP2/

Note that there is a separate example for the W and non W LED, for non-W it is:

cp blink/blink.uf2 /media/$USER/RPI-RP2/

Also tested the UART over USB example:

cp hello_world/usb/hello_usb.uf2 /media/$USER/RPI-RP2/

You can then see the UART messages with:

screen /dev/ttyACM0 115200

TODO understand the proper debug setup, and a flash setup that doesn't require us to plug out and replug the thing every two seconds. www.electronicshub.org/programming-raspberry-pi-pico-with-swd/ appears to describe it, with SWD to do both debug and flash. To do it, you seem need another board with GPIO, e.g. a Raspberry Pi, the laptop alone is not enough.

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