discrete mathematics – average of the application of the pigeon hole principle

Arrange 0-9 on the circular table
There is a section where the sum of three adjacent numbers must be 14 or more

I know we can solve this problem using the pigeon hole principle

I know the dovecote is number 10
I want to know why we have to add 0 + 1 + .. 9 = 45 x 3 = 135

And divide it by 10 = 13.5

Is this the right way to solve this problem? If yes, I want to know why we have to find the average?

Obtain a clear image for a paper with a 7.62 mm hole located at 50 m

I'm going to assume that you only want to count the holes on a paper target and know their approximate location.

7 mm at 50 meters is 0.008 degrees.

Then we have to make some assumptions about the camera. I will be using my equipment, a Canon 7D, APS-C (1.6 crop sensor), of around 5000 pixels on the long side.

I would like the holes to be around 10 pixels wide, this is an estimate of how important you need the holes in the camera frame.

10 pixels / 5000 pixels = 1/500 of the frame

0.008 degrees * 500 = 4 degree field of view

You can achieve this with a 400mm lens, these are fairly common and a decent good is $ 1,000 to $ 2,000. See this calculator.

Note that your field of vision will be 2.8 x 1.8 meters. It’s probably bigger than your goal. If you want the target to fill the camera frame, the calculation will be different.

Edit: test the image. 3.5 mm hole at 25 meters. I can't easily walk 50 meters.

Canon 7D, zoom 100-400 f5.6 M1 @ 400 mm, f8, remote flash.

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Zoomed to display the actual pixels:

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mp.mathematical physics – Is the Wikipedia representation of the ergosphere of a black Kerr hole a Cassini oval?

Warning: this is a cross article from MSE, where this question was asked on November 4, 2019 and has so far received no positive votes, no comments, and no responses. .

By taking a look at https://en.wikipedia.org/wiki/Rotating_black_hole (revision in progress), I thought that the boundary of the ergosphere appearing in the photo at the beginning of the article considered looks very much to a Cassini oval. Is it really one? If so, how do you prove it?

Databases – Need to understand the security hole?

I create an encrypted value database.


Suppose I store "John" which would be encrypted and stored under the name "Yoky".

John | Yoky

Now, I'm storing "Johnny" that would be encrypted and stored as "Koaddy"

John   | Yoky

Johnny | Koaddy

Now, with the above storage, I will not get any type of regex search feature. If I wanted to look for "Jo%", it will not work.

But if I store the values ​​after breaking them. as

Jo      |   Yoky , Koaddy
Joh     |   Yoky , Koaddy
John    |   Yoky , Koaddy
Johnn   |   Koaddy
Johnny  |   Koaddy

Here, regular expression searches will work "Jo%", "Joh%" will give both Yoky and Koaddy what I want.

I can see the obvious security hole above that everyone can trace Jo, Joh.

I have therefore decided to store the encryption of these.


I will AES encrypt my stumps and store them.

qkjklewr!j==      |   Yoky , Koaddy
klkadsopos==      |   Yoky , Koaddy
oensd%21op==      |   Yoky , Koaddy
kaknvp23b02==     |   Koaddy
kashdi2094j==     |   Koaddy

When you perform a search type, for example "Joh", I will first encrypt "Joh" and then perform the search. Therefore, it corresponds to the AES numerical value of "Joh", ie klkadsopos ==


Note: The column will use different keys and algorithms to protect the data.


Note: This storage will be encrypted TDE.

I must understand if I'm missing something fundamental here.

database design – Need to understand the security hole?

I create an encrypted value database.


Suppose I store "John" which would be encrypted and stored under the name "Yoky".

John | Yoky

Now, I'm storing "Johnny" that would be encrypted and stored as "Koaddy"

John   | Yoky

Johnny | Koaddy

Now, with the above storage, I will not get any type of regex search feature. If I wanted to look for "Jo%", it will not work.

But if I store the values ​​after breaking them. as

Jo      |   Yoky , Koaddy
Joh     |   Yoky , Koaddy
John    |   Yoky , Koaddy
Johnn   |   Koaddy
Johnny  |   Koaddy

Here, regular expression searches will work "Jo%", "Joh%" will give both Yoky and Koaddy what I want.

I can see the obvious security hole above that everyone can trace Jo, Joh.

I have therefore decided to store the encryption of these.


I will AES encrypt my stumps and store them.

qkjklewr!j==      |   Yoky , Koaddy
klkadsopos==      |   Yoky , Koaddy
oensd%21op==      |   Yoky , Koaddy
kaknvp23b02==     |   Koaddy
kashdi2094j==     |   Koaddy

When you perform a search type, for example "Joh", I will first encrypt "Joh" and then perform the search. Therefore, it corresponds to the AES numerical value of "Joh", ie klkadsopos ==


Note: The column will use different keys and algorithms to protect the data.


Note: This storage will be encrypted TDE.

I must understand if I'm missing something fundamental here.

malware – What was the security hole in WhatsApp operated by NSO?

Vulnerabilities such as BroadAnywhere and StageFright were identified and corrected a few years ago, and any self-respecting company would have taken note of this and would have scanned its software for similar bugs. So, I am not very convinced that the so-called zero-day exploit of WhatsApp was something unknown for the company.

What was the security breach? Was it similar to StageFright, where a subflow / overflow allowed the injection of malware? Could it be an intentional backdoor introduced by the parent company to read messages (like how they stored passwords in plain text), and NSO (or any random hacker) would have it's windy?

[ Astronomy & Space ] Open question: Is it possible to escape a black hole?

[Astronomy & Space] Open question: Is it possible to escape a black hole? .

[ Politics ] Open question: My girlfriend has a hole in the wall, should I break up with her?

[Politics] Open question: My girlfriend has a hole in the wall, should I break with her?

5th dnd – What is the orientation of the Rope Trick hole?

The chord spell specifies

Holding one end of a rope 60 feet or less causes the other end
climb until the rope is completely perpendicular to the ground. the
high-end, a portal opens on an extradimensional space in which eight
medium or small creatures can adapt by climbing the rope. The rope
can also be dragged into the space to hide the entrance and the
the portal itself is invisible.

Spells and attacks are unable to enter or exit from the extradimensional
space, but those who are inside can see through a distance of 3 feet by 5 feet.
window centered on the top of the rope.

If anything inside the extradimensional space has not come out
before, he will fall at the end of the spell.

Our group played on the assumption that the window is positioned vertically in relation to the ground plane, because it is so that most of the windows we see are positioned. This means that you climb into the hole as at the top of a cliff at the end of the rope and then you have a view of the world as if you were looking through a normal building window.

However, this seems to be in contradiction with the popular representations on the Internet.

The difference would be surprisingly relevant for some of the standard strategies we have used.

How is the Rope Trick Portal positioned relative to the ground / gravity / rope plan?

35 mm – Canon AE1 rewind crank screw hole program, which size?

I have a Canon AE-1 program with a crank with a missing rewind. Can not find a substitute anywhere online, thinking of trying to fake something by myself. There is a threaded hole in the center of the ASA selector where the crank would go. What size of bolt / wire would it be?

Plus, in case I just want to buy many sizes to test, do Canon cameras use metric or imperial locks?

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