Could you explain the meaning of warlock invocation number next to its grade?

I am rolling a warlock in my current campaign and we started at level 3. For my invocations, I have picked walk unseen and fell flight. I was told I could not do that by my DM since he told me my level wasn’t enough. However, when I referred back to my Complete Arcane, it mentioned:

A least invocation has a level equivalent of 1st or 2nd; a lesser, 3rd or 4th; a greater, 5th or 6th; and a dark invocation has a level equivalent of 6th or higher (maximum 9th).

So I automatically assumed that at level 1 and 2, I have access to least and 3 and 4, I have access to lesser, turns out not.

When I refered back to Complete Arcane for the invocations I picked, it said:

Fell Flight: Lesser; 3rd

and

Walk Unseen: Lesser; 2nd

I am really confused about which level can I pick these two invocations? I would appreciate it if you could explain how the warlock level corresponds to the invocation grade and the number next to it.

Please explain me this question in very simple terms

Consider the following snapshot of a system running n processes. Process i is holding Xi instances of a resource R, 1 <= i <= n. currently, all instances of R are occupied. Further, for all i, process i has placed a request for an additional Yi instance while holding the Xi instances it already has. There are exactly two processes p and q such that Yp = Yq = 0. Which one of the following can serve as a necessary condition to guarantee that the system is not approaching a deadlock? (A) min (Xp, Xq) < max (Yk) where k != p and k != q (B) Xp + Xq >= min (Yk) where k != p and k != q (C) max (Xp, Xq) > 1 (D) min (Xp, Xq) > 1

Can someone explain exactly how Facebook hacked and intercepted a text message?

I have an Android phone (Blackberry KEY2). I do not have the Facebook app installed on it. I did log onto Facebook once on it via the Chrome browser to confirm it worked.

The other day, I responded to my granddaughter’s request for a video chat via Facebook for kids using my laptop. Apparently, all the kids her age (5 yrs old) are chatting with each other because of staying at home because of coronavirus. While in messenger, I briefly noticed a text message from a friend whip by. It was probably on the Facebook page (I didn’t have anything else open and video chat was smaller than the other page, overlapping a good part of it).

After the video session, I couldn’t find the text message anywhere. I emailed him back and he said he did not send it over Facebook, he just sent a text from his cell phone. I checked my phone, and yes it was there as an unread text message.

I am now perplexed, I never associated my cell phone number with anything in Facebook. I hardly ever use Facebook. So how would Facebook know to intercept a SMS message and display it via my Facebook page on my laptop?

What’s more, I don’t have any other app on my laptop that is aware of my cell phone number, especially anything that was running.

I went through my profile on Facebook, and my cell number does not show up in it at all.

It looks to me like Facebook has somehow, surreptitiously associated my cell phone with my account. Is anyone else aware of anything like this? How do I get my cell phone number disassociated? If I do not use the Facebook app, what other data could Facebook steal from any device (phone or computer) via a browser? Or, could anyone point to where text messages are supposed to be found within Facebook via a browser?

Explain the equation to find the collaboration between neighbors in SOM in unsupervised learning

In kohonen SOM algorithm, the equation to find the collaboration is:

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I know that LDist is the lattice distance and sigma is the standard deviation. I am just wondering why they are squared ? Can anyone help me to visualize the equation or explain to me what is going on in the above equation ?

What can cause low cost and high runtime in EXPLAIN ANALYZE?

I have a database that pretty consistently runs queries in a magnitude of cost/10 ms. There are a couple queries where EXPLAIN ANALYZE reports a cost of 2000 (which I’d expect to be somewhere in the ballpark of 200ms) but runs take multiple minutes.

My first thought is that some other activity is bogging down postgres causing this (either other processes on the machine or concurrent database activity). Is there anything else I should be looking into? Am I mistaken to expect similar cost:time ratios for different queries?

How to correctly interpret index usages from EXPLAIN of mysql?

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I’ve exported the results of an EXPLAIN run on a query. What I find confusing is that there’s the key column listing out one of the indexes from the list of possible_keys(not shown in picture) however only the top row makes mention of Using index explicitely in the Extra column.

  1. What does this mean in the 2nd row, is it not using the index listed in the key column?
  2. How should I interpret what the contents of the key column is about and how it is used?
    enter code here

    a. Should I interpret this as that index is used in the where stage of this query?

Can someone explain what the “Proficiency Bonus” is in D&D 5e/Next exactly?

I am reading the 5e rules, and I keep seeing how you can add proficiency bonus to attack rolls checks with weapons you are proficient in and skill checks in skills you are proficient in, but I can’t find anything on what this bonus actually is. How do you determine what the numerical actual bonus you add to your roll is? And at what times is it used?

Please explain how backup codes work in TOTP, like google Authenticator

My understanding is that in TOTPs are like HMAC where code is derived from time.

However, I am struggling to understand the concept of Backup Codes in google Authenticator , and how are they calculated as they are not time sensitive and can be used in any sequence . So how google has implemented that? Thanks