Context free languages invariant by “shuffling” right hand side

Given a grammar for a Context Free language $ L$ , we can augment it by "shuffling" the right hand side of each production, e.g.:

$ A \to BCD$ is expanded to $ A \to BCD \; | \; BDC \; | \; CBD \; | CDB \; | \; DBC \; | \; DCB$

It may happen that the resulting language $ L’$ is equal to $ L$

For example:

Source               Shuffled S -> XA | YB         S -> XA | AX | YB | BY A -> YS | SY         A -> YS | SY B -> XS | SX         B -> XS | SX X -> 1               X -> 1 Y -> 0               Y -> 0 

Is there a name for such class of CF languages ($ L = \text{shuffled}(L)$ ?

Does RLNC (Random Linear Network Coding) still need interaction from the other side to overcome packet loss reliably?

I’m looking into implementing RLNC as a project, and while I understand the concept of encoding the original data with random linear coefficients, resulting in a number of packets, sending those packets, and thus the client will be able to reconstruct the original data from some of the received packets, even if a few of the packets are lost, if enough encoded packets have arrived to create a solvable equation system.

However, I have not seen any mention of the fact that if there is a non zero percent of packet loss, there is a possibility that the receiver of the encoded packets will not receive enough packets to reconstruct the original data. The only solution I see to this is to implement some type of sequencing so that the receiver can verify he hasn’t missed some packets that would allow him to reconstruct the original data, in other words interaction. Am I missing some part of the algorithm or not? If someone has solved this problem already, can you please show me where it has been solved so I can read about it?

The Other Side of CAPTCHA [closed]

CAPTCHA stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart", but we only consider one half of it i.e. a test to separate genuine humans from bots.

Can a program/test exist that can be only "solved" by computers/bots and not by humans?

If not, what prevents such a program from existing in the foreseeable future?

If it does, could you please cite it and how it works?

Note: The Voight-Kampff Test by Phillip K Dick still has its drawbacks.

SSL Cert for client side web application, is it needed?


I have tried to find good answer for it, but I haven’t gotten good article about this topic.

Since there are 2 types of client applications (in bigger picture) – one that runs on server and one that you download and runs in your browser.

My question comes in about the one, that runs in your machine (that you download at first visit – Blazor WebAssembly to be specific).


Do I need to enable SSL (HTTPS) for this application or web server, that hosts this application as well or is it not needed in the end?

Does only having API connection encrypted be enough?


Yes, this is a cost saving masure, since this is for my hobby project and I would like to keep running costs as minimal as possible. But since I still exchange data, that should not be seen by 3rd party, this application needs to be secure.

To enable HTTPS I would need second Static IP, which is 3$ a month (which is not much), but again, it is additional cost for me, that I would rather not have.

Return once more to the Light Side

In my campaign a level 13 paladin PC is about battle a blackguard. Eventually, the paladin will realize the blackguard is a former colleague who fell from grace. I’m sure the player will want to turn the blackguard back to the side of good again after the blackguard is defeated.

Can a blackguard regain his good alignment? If the blackguard does become good, what happens?

Best way to make a Side Panel UI with Libgdx? (Java)

Take this image for example, the game is called Realm of the mad god, and it has this side panel filling the whole screen height with the player info.

To reproduce it, Is there any way to make the game "view" smaller so I can fit the side panel to its right without literally overlaying the game, PROBABLY like this game did, or is the only way out to overlay the game?

(Tibia might also be an example of a game smaller then its UI)

Side Panel example