Turing machine on input w tries to move its head past the left end of the tape

Consider the language

$ $ L = \{ \langle M,w \rangle \mid \text{$ M$ on input $ w$ tries to move its head past the left end of the tape}\}. $ $

Prove whether L is decidable or not.

I tried to prove it as undecidable through reduction method but could’nt reduce the language halt to L inorder to prove that it is undecidable.

What is the name of this Ravenloft adventure where imprisoned PCs control NPCs in the past?

In this Ravenloft adventure, PCs suddenly find that they are now inhabiting the bodies of unknown characters at a ball held, as far as I remember, by Strahd von Zarovich at his castle.

How is this adventure called?

I remember the adventure being crudely formatted, so I’m not entirely sure it was an official one, but I’m writing anyway hoping that it was.

Am I the only one who can’t help but constantly think back on all the horrible security nightmares (and potential ones) from my past? [closed]

I’m not going to go into any specifics here, because I’ve learned that “certain” open source projects are extremely sensitive about any criticism and will defend any kind of madness by blaming the user for not fully reading and comprehending the often extremely cryptic and ambiguous manual, while not putting any blame on the software for allowing the insecure configuration in the first place.

You may think I’m joking, but even 15-20 years later, I still have actual nightmares about things which happened, or could have happened, or may have happened without me ever finding out, in the past, due to bad security, either by myself and others (affecting me).

A huge issue with security is not realizing one’s own limitations and having a big ego. You know how it is: you are 15-16 and you are totally an “1337” cracker, aren’t you? Everyone else is stupid and you know everything. You couldn’t possibly misconfigure or misunderstand anything, right? That manual only seems to verify what you already knew… yes, that seems to be correct… yes, now let’s put it live! It’s rock-solid!

… and then it turns out that somebody has been remotely connecting from across the world to your ultra-sensitive database for the last eight months and saved all your private information to blackmail you perpetually. Because it allowed any password as long as they guessed the default admin account. Which was supposed to only be accessible from

The most frustrating part is perhaps that, now that I know about many of these things, I find it utterly impossible to educate others about it. They are just as deaf to my advice as I would’ve been to advice from others back when I thought it was a good idea to enable that stupid mode which bypasses all passwords, because even though I read the manual, I read it horribly wrong!

I actually remember saying to myself: “Well, they can’t mean that ANY password goes, because that would defeat the entire purpose of having passwords in the first place, so I can safely conclude that they didn’t mean this.”

They meant it.

Not one day goes by without me thinking back on all these stupid decisions, and while I know very well that it does me no good, I can’t help but be bombarded with these memories and thoughts. It’s easy to laugh at it now and shake one’s head, but when I saved the config that fateful day and reloaded the service in question, I was 100% convinced that my database was fully locked down and that I was the only person in the world who would ever be able to access it, because I had read the manual as I was always instructed to do.

The above vague story is just one out of many such cases which I’ve experienced or heard of. Somehow, these experiences make me fully understand how there can be almost daily news of major critical databases exposed to the Internet with no password. They were simply set up by people who just didn’t understand what they were doing, and I consider it unfair to put all the blame on them.

I think a lot of software is made with a strange attitude to security, where you are harshly punished for not knowing everything about the software, as the developers (but nobody else) does.

when connecting to someones wifi without using it, can they see search history from the past? Please answer it’s important for my work

We visited a friend who’s working as a programmer, And he told me to connect my phone to his wifi so he could send me a picture, however he didn’t send it and I left my phone connected to his wifi for an hour without using it. He caused me a lot of problems in the past but we forgot about it.

I really suspect what happened and I wanna ask you of he can see my search history, notes, pictures, messages, passwords? Or install a spyware in my phone? Just via wifi even if i didn’t use it to open anything?

Please answer my work depends on this.

What spells allow character’s to see past events?


The wizard in my campaign has a personal quest to stop the ‘dark magic’ that destroyed his home town. However his character knows very little of the details of exactly what happened. He was in the library studying (typical wizard things) during the event and only saw the aftermath. So during the campaign he has been seeking out places of magical learning that can help him learn what happened to his home.

As a source of information I came up with the idea of giving him some spell or ritual that he could use when he returned to his home town to gather information. I expect the party to be around 9th level when they gain this ritual. Ideally it would allow him to relieve the event as though he was there and gain first hand information. The event to be relived will be at least 3 years in the past by this time.

What I want

Ideally I am looking for a spell with the following criteria:

  • 4th or 5th level and on the wizard spell list
  • Has a high but achievable material component cost (~1000gp)
  • Casting time between 1 min and 8 hours
  • Allows the caster to relieve past events at their location

Close but not perfect

So far I have found three spells that fit some but not all of the criteria:

  • Ears of the City (Player Companion: Heroes of the Street)

    • As a 1st level I feel this too easy for a major plot point in this character’s story. I worry that is won’t feel like a proper achievement to gain this spell.
    • Spell relies on diplomacy/perception checks neither of which this player is strong in so could be unreliable.
  • Legend Lore (Core Rulebook pg.304)

    • Details are very vague for what the player is trying to obtain. I know this is almost entirely up to the DM and I can make it work but I’m not sure the information they are seek would be called “legendary”.
    • Resource expenditure is good, I would like this be something the players have to work/plan for.
    • As a 6th level it is higher level than would be available at the time. Though a scroll or something could easily bypass this.
  • Retrocognition (Occult Adventures pg.185)

    • This probably has the best flavour of what I am going for. Psychic impressions that go further back the longer you concentrate for is great.
    • As a 7th level spell is it beyond the reach of the party without giving them a scroll.
    • Caster level limitations in the spell will make it difficult to see back far enough. 1 hour/minute is very slow, even the 1 week/minute at 13th level would make this more useful but my players are unlikely to be that high when using this.


Before I try to choose one of these spells, modify one or homebrew something entirely from scratch. I wanted to draw on the community wisdom for more information.

Are there any spells that allow a creature to see the past other than those I listed?

Answers don’t need to meet all of my criteria above anything that meets the general goal is useful inspiration. If someone does find the perfect spell I will probably bounty it for being awesome.

calculating days past since creation time based upon the real todays date changing daily

Does anybody know a way of showing days past on view (rendering of a page), since the day an item was created.

I need this number for other calculations, to color format some usefull output.

I see a lot of example, mainly telling that [today] / today() can’t be used for that in calculated columns, some work around that require the item to be modified, but that’s not what i want, i like to show, when items are not modified. and people are late to respond i need to show that.

–update– This problem seams a bit more complex then i originally thought. As i wrote i want to see how long it takes before people respond. There’s a status(text) and modified(date) column, once text changes to it should stop counting, and preferably another column starts to counting between status assigned and status closed. (modified date might not be the best indicator for this is the status column, as modified might not always work(people need to have opened it). FYI there is also another column with a closed date, and closed is a status as well, so closed date could be retrieved from it.

Therefore i think client side rendering would not solve this. Yes those scripts work to so show days since, but at some point they should stop counting, i dont think i could do that with client side rendering

So i think i should do some kind of server side powershell script, and schedule it to run each day at 00:01 (not the best option perhaps but right now i dont know other solutions to this).

How can I get past the blank purple screen on my Ubuntu 18.04 LTS system?

After coming back from a 2 week holiday, I discovered that I couldn’t get to my desktop PC’s Ubuntu desktop. After entering user and password information, the information is accepted but the screen becomes a blank purple, and the mouse disappears.

What I’ve tried so far: 1. I can boot into CLI by adding a ‘3’ to the appropriate line in grub. 2. I can log in remotely via ssh. 3. I can get a remote desktop GUI.

What hasn’t worked: 4. Adding ‘nomodeset’ to the linux line in grub. If I do this, my screen goes black after logging in. (I can still SSH in and RDP in.). If I press the return key, I see a white X in the middle of the screen. I can get a shell with Ctrl+Alt+F3. 5. I messed about with recovery mode, but it didn’t seem to help.

System is fully updated including new kernels (I now have kernels 5.0.0-27, 5.0.0-25, 5.0.0-23).

My system: Dual boot Ubuntu 18.04.3 LTS & Win 7. Ubuntu has ubuntu-drivers-common installed.



How to retrive past transaction values or data from the ethereum contract?

I have made one contract where I have taken a string name. I have updated this string name three times. 1st – Mike 2nd – Ronaldo 3rd – Tyson

Now, I want to extract past or old transaction data from ganache-cli. I am able to extract the recent name “Tyson” but I want to extract previous data which was stored in ethereum.

I tried using web3.getaTransaction(), I am getting everything like a nonce, block number, but data is in encrypted form.

Can anyone please suggest me, how to retrieve the older transaction data?