Is it decidable whether Turing Machine never scans any tape cell more than once when started with given string

The problem:

Is it decidable that the set of pairs $ (M,w)$ such that TM $ M$ , started with input $ w$ , never scans any tape cell more than once.

How can I easily prove above to be decidable. I found following proof confusing:

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How is $ l+m$ is upper bound on number of steps? I feel we should be doing at least $ l\times 𝑄\times \Gamma\times\{𝐿,𝑅\}+1$ steps ($ Q$ being number of states,$ \Gamma$ being set of tape alphabet, $ l$ is string length, $ L$ and $ R$ are head movement directions).

Is it decidable “Given a TM M, whether M ever writes a non blank symbol when started on the empty tape.”

I came across below problem in this pdf:

Given a TM M, whether M ever writes a non blank symbol when started on the empty tape.

Solution given is as follows:

Let the machine only writes blank symbol. Then its number of configurations in the com computation on w is q × 2, where q is the number of states of M; the factor 2 is for the choices re. the direction of heads movement; there is no factor for the written symbol because that is always blank. So the problem is decidable, decided by the following machine: input (M,w), run M on w for q × 2 steps; if it M ever writes a non blank symbol, stop with yes answer; if M never writes a non blank symbol, stop with no answer


Q1. How be sure all q x 2 configurations will happen while running q x 2 steps on w? Some configuration may get repeated in q x 2 steps.

Q2. Question says “when started on the empty state”, but the answer tried to simulate TM on non empty string w. How does it makes sense?

Playing on IRC, getting started [on hold]

I live where no tabletop has ever been played, thus I had to search elsewhere for some games, namely the Internet. I’ve spent a lot of time browsing the web but the best communities I could find were filled with young, Anime-obsessed fellows.

I am looking for a serious, immersive game, but I know nobody and I don’t know where to find players. Do you know any good IRC networks/channels for roleplayers? I am totally clueless as to where I should get started, my experience with RPGs is extremely limited and the sea of web pages I’ve visited aren’t helping. I refuse to believe that the Internet isn’t some kind of gateway for RPG players from all over the world so please, can someone help me out?

Additionally, if you know some good play by post communities, you might as well tell me. I’ve read other answers (like How can I find PBP games? – now deleted, 10k rep only) but I’d like to hear from someone with some experience on those sites rather than just a list of names.

Black Screen with cursor blinking when started Ubuntu on VirtualBox

Ubuntu on my Virtual Machine was running fine when I restarted then suddenly it starts showing a black screen. I googled and tried multiple solutions like:

  1. by disabling the “Enable 3D acceleration” on virtualBox settings
  2. Enabling the “Intel Virtualization Technology” from BIOS

Please note, when I used backup Ubuntu, it works fine. My host system is Ubuntu 18.04.3 LTS. VirtualBox Version 6.0.12, Ubuntu guest OS in VirtualBox is 18.04.2.

I will appreciate if you can help to address the issue

Getting started with SharePoint apps/add-ins

I recently tried to evaluate SharePoint apps/add-ins as a solution for a client (after having failed to find a quick solution with MS Flow), but I couldn’t find good resources (YouTube, web posts) to even get started.

I’d like to know what they do, what they don’t do, how they are accessed, how to create them, etc. Do you have any good resources? Any format welcome

Need help getting started

The company I work for just dove into the deep end of internet advertising. The video ads that run on Hulu, YouTube pre-roll, ect. I’ve got down fine. Banners are where I need some direction.

The sales team wants robust, interactive, motion driven ads. Right or wrong that’s what they want. On my end (the design end) I’m dealing with Google restrictions of 150kb or less and no more than 5FPS.

I see these robust ads all over the place so I know that there are ways to do this but I’m very new in it. Maybe it’s better to say that so much has changed and passed me by since I left web design to focus on video.

So here’s the question

I’ve picked up the word "Ad Tags" as a possible solution but am not very sure how that works or if it’s even the right solution. Can anyone point me in a good direction of what programs/language are best for creating these ads and the best way to serve them in a way that they will be accepted. I really need "creating interactive/motion ads 101", but I don’t even know the lingo well enough to know where to start looking.

Thanks in advance for any input.

18.04 Boot freezes at “Started Hold until boot process finishes up” boot reboot, FYI I’m not using ubuntu as dual

I tried to install some updates and after that when I rebooted the laptop it runs some commands and at last shows “Started hold until boot process finishes up. ” Ctrl+alt+f2 opens command line but there is no display whatsoever. I tried recovery mode and deleting some files but that is of no use as I already had enough memory. Please help thanks in advance.

SharePoint 2013 – One or more services have started or stopped unexpectedly – SPTimerV4

I’m getting this error message in CA. I checked the timer service and it is up and running. I tried with “Repair Automatically” but use.

ULS Error

The following services are managed by SharePoint, but their running state does not match what SharePoint expects: FIMSynchronizationService. This can happen if a service crashes or if an administrator starts or stops a service using a non-SharePoint interface. If SharePoint-managed services do not match their expected running state, SharePoint will be unable to correctly distribute work to the service.. Automatic repair is being attempted.