The using of has and have in question
Does it have or has?
View a man page in a specific section I wanted to access man pages for command chmod.  Command whatis chmod gave this output:  chmod (2)            - change permissions of a file  chmod (1)            - change file mode bits  But I was actually looking for chmod(2).  When I type man chmod, man pages for chmod(1) appears.   Both man chmod(2) and man 'chmod(2)' commands show error.   I tried running info coreutils 'chmod invocation', but output is some kind of documentation which doesn't look like a typical man page. Do multi-use keys get discarded when finished with? As with many resident evil games, you sometimes needs to collect certain keys to open certain doors, and resident evil 7 has plenty of these around.  Some keys are clearly single use, and get left in the lock in which you use them. However, there are a number of keys that can be used on multiple doors. For example, the Scorpion Key.  I am concerned that I might end up carrying these around needlessly and using up valuable inventory space, so...  Do these multi-use keys get discarded when you use them on all the doors they apply to? Or do you get a warning saying the key is no longer needed? (like previous games are known to do) Exponent and abelian groups What exponent $e$ can guarantee the group to be abelian? Are there any known results except the case $e = 2$? Thanks for help. Holmby Hall is a landmark site in Los Angeles. The Wikipedia page doesn't use "the" before Holmby Hall, but has used the before The Fox Theatre. This story was in one of the first SF anthologies I ever read, in the mid-1960s. A meteor lands near to a house. The householder finds it and carries it into his house (meteor is grapefruit/football sized). It’s actually a crashed spaceship, crewed by beings the size of beetles or cockroaches. They emerge, and are spotted by the householder, who of course thinks they’re insects, but notices one seems to be holding a tiny tube. He reaches towards it and the alien shoots his hand (the tube being a gun, of course), stinging him. I can’t recall how the story ends, but I’d love to know what the story was called, and who its author was, as I’m trying to assemble a list of the early SF that fired my enthusiasm for the genre. Show that $d_2$ defined by $d_2(x,y)=\frac{|x-y|}{1+|x-y|}$ is a metric I want to know the memory usage of my Python application and specifically want to know what code blocks/portions or objects are consuming most memory. Google search shows a commercial one is  (Windows only).  And open source ones are  and .  I haven't tried anyone, so I wanted to know which one is the best considering:   Gives most details. I have to do least or no changes to my code. display only 3 foreach result per row Active login not recognized on Super User What is the best regular expression to check if a string is a valid URL? How can I check if a given string is a valid URL address?  My knowledge of regular expressions is basic and doesn't allow me to choose from the hundreds of regular expressions I've already seen on the web. Is there a difference between "think of something" and "think about something"? I've also met "have heard of/about something". Otherwise, is there any alternative command line utility that can achieve this? Thick annulus (ring) in 3D I have a machine running a couple of vagrant VM. The problem I have is that sometimes I forget to shutdown those VM before I shutdown or reboot my machine. Because of that my machine get stuck with this message: waiting for vboxnet0 to become free  I searched about solutions and I found this page :    I tried what they for shutdown, but it doesn't work.  I wrote an sh file for that command:  #!/bin/bash  cd ~/workspace/git/mediaservice vagrant halt   any suggestions? find out which program pops up a command line window I have windows 10 home and from time to time I see a command line window popping up for less than a second. I want to find out which process is causing that. It's not very often that this window pops up so I need some tool that can run for a long time.  Does anyone have a good idea?  Regards Tobias General integral to find resistance My question is: is there a simple and truly general equation for the resistance between two electrical equipotential surfaces?.  Obviously, if so, what is it, and if not, why?  It would be very difficult to solve, granted, but I just want to see a calculus equation that is fully descriptive.  I have two frameworks under which this could be entertained, I'll write those out and then explain the motivation.  To start with, we need propose that the volume separating the two surfaces has a volumetric resistivity, $\rho$ in units of $(\Omega m)$.  Single Volume Framework  We can limit the discussion to a defined volume, then the surfaces reside in that volume or on the surface of it.  This volume may have a constant resistivity $\rho$ while everywhere outside the volume is completely electrically insulating.  Infinite Volume Framework  An alternative to the above approach that might make the task more or less difficult would be to replace a constant resistivity with a spatial dependence $\rho(\vec{r})$ and no longer require a boundary condition.  In that case we only have 3 mathematical inputs to the problem, which is the resistivity defined for all $\vec{r}$ and a definition of the two surfaces, $S_1$ and $S_2$.  Known Algebraic Analogs  The  that I find insufficient is:  $$R = \rho \frac{\ell}{A}$$  Where $l$ is the length of the restive material that is any shape which has translation symmetry over that length, and $A$ is the cross-sectional area.  Obviously, this is a rather simple equation that won't apply to more complicated geometry.  Even more  seem to give equations that fall short of what I'm asking.  For example:  $$R = \rho \int_0^l \frac{1}{A(x)} dx$$  I think it's obvious that an equation such as this is built upon a myriad of assumptions.  For a thought experiment, imagine that the area starts out as very small and then pans out to very large quickly.  Well, accounting for the larger area in the above sense underestimates the resistance, because the charge has to diffuse out perpendicular to the average direction of flow as well as parallel to it.  I have some reasons to suspect this might actually be rather difficult.  A big reason is that all the approaches I'm familiar with require the flow paths to be established beforehand, which can't be done for what I'm asking.  So maybe this will result in two interconnected calculus equations.  Motivation  I had an interest in , and it occurred to me that I can't quickly and simply write down the equation for resistance between two points.  The unique thing about Squishy Circuits is that it calls for two types of dough, one that conducts and one that is mostly insulating.  However, the recipes aren't perfect and because of that, the young children who play with these circuits regularly encounter the limits of conductor and insulator definitions.  If you make your conductor dough too long and/or too thin, you will encounter dimming of the light you connect with it.  Similarly, a thin insulator layer will lead to a lot of leakage current which also dims the light. Which is the easiest way to evaluate $\int \limits_{0}^{\pi/2} (\sqrt{\tan x} +\sqrt{\cot x})$? What is an effective way to level Archery? Can the Earth's magnetic field be used to generate electricity? How to remove configuration files completely Recently I uninstalled some software using sudo apt-get --purge autoremove, thinking that this would remove all traces of it including unused dependencies and configuration files. However I discovered that a configuration file was left behind in my home folder.  Is there a more powerful command which would remove even that?   Also, is it safe to delete the hidden files and folders under home, if they are merely configuration files, or are there other kinds of files?