One definition of can in Merriam-Webster Online is:     c —used to indicate possibility &lt; do you think he can still be alive> &lt; those things can happen> ; sometimes used interchangeably with may   But in The Elements of Style written by William Strunk, Jr., it says:     Can. Means am (is, are) able. Not to be used as a substitute for may.   This contradiction makes me confused. So in what situation can can be used "interchangeably" with may, and in what situation it cannot?  EDIT: The two sentences in The Elements of Style make me feel that the author permits only one use of can (be able) in the first sentence and proscribes the other use (may; to indicate possibility) in the second sentence. Did I misinterpret the author's meaning? Or the text is ambiguous?
Which is correct if I want to request for a pen?        Can I have your pen please?   May I have your pen please?
I am trying to calculate the final velocities of two equal mass 2-dimensional circles after an elastic collision. I have tried to figure it out using formulas I know from high school physics, but nothing seems to work. My known variables are:   initial x and y velocities for each circle x and y distances between the centres of the circles at the time of the collision   The variables I would like to solve for are:   final x and y velocities for each circle   Here are diagrams showing all the variables: What is the difference between a deep copy and a shallow copy? "She need not worry" or "she needs to not worry"? I just came across this weird use of &quot;need not&quot; on :  Madam/sir, My daughter is stuck in Uk . She has lost her  . She is difficult to return back India home [sic]. Please help  In response,  says:  She need not worry. She should stay where she is. Just tell her to keep herself safe. Please delete your tweet.  Shouldn't it be &quot;she doesn't need to worry&quot; or &quot;she needs to not worry&quot; given that the subject is &quot;she&quot; (singular)? Or is this some kind of grammatical construction I don't know? I believe who wrote it was a native speaker of English and they might be correct. Can someone explain this please? How to implement "select all" check box in HTML? What does the TLS 1.2 client finished message contain? I am implementing TLS 1.2 and I'm stuck on the client finished message.   My question is: what is the size and structure of a clients finished message in TLS 1.2 when using the ECDHE_RSA_AES_128_GCM_SHA256 cipher suite.   I searched for this question and someone somewhere stated its size is 48 bytes; more specifically:   12 byte verify data 1 byte handshake type 3 byte verify data length and 32 byte MAC   Is that really correct?   I mean: according to  finished messages have {verify_data[verify_data_length]} and verify_data = PRF(master_secret, finished_label, hash(handshake_messages). Also, according to RFC 5246 section 5 PRF(secret, label, seed) = P_&lt;hash&gt;(secret, label+seed) and P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed). So, when I compute HMAC using SHA256 for verify_data its size is 32 byte.   As a result, I'm a bit confused in relation to the verify_data size and the finished message structure. Can anyone help me to understand this and/or maybe put me on the right track somehow? Postgres: Reclaiming Space How to urlencode data for curl command? I am trying to write a bash script for testing that takes a parameter and sends it through curl to web site.  I need to url encode the value to make sure that special characters are processed properly.  What is the best way to do this?    Here is my basic script so far:  #!/bin/bash host=${1:?'bad host'} value=$2 shift shift curl -v -d "param=${value}" http://${host}/somepath $@ I recently ordered the GTA V PC from Steam and when I finished installing and launch the game. It gave me "Grand Theft Auto V has exited unexpectedly". I tried "safe mod" and every option available, but none of them work. I checked some forums and found a lot of people having the same problems. What could be the possible cause? I'm using a laptop with these specs:  CPU: i7 4700m GPU: AMD HD8970M RAM: 8GB  I'm pretty sure my laptop is way beyond the minimum specs. Does someone know how can I enter the game? Photoshop: How to draw a guide with an exact distance from another guide Before drawing, I want to draw all guides for my layout. For example, I have a guide line named A already. After that, I want to have another guide named B  parallel with guide A and at 50px distance from it.   I have three solutions:   Draw line B and by "some way", I can see the current distance directly when I'm drawing, so I can make the distance exactly what I want it to be.  Draw line B. And then I use the Ruler tool to see the distance between the two guides. This method has disadvantages: maybe the ruler line that I draw isn't perpendicular with the guides and I'm not sure when the distance is enough. There are other clever ways, that help me get this job done fast and easily, but that I don't know yet. I think Photoshop should support this feature.   What is the best way to achieve this? I am investigating the vulnerability to  and I think I understand how and why this sort of attack works.  What I don't understand is why Lighttpd and NginX are not affected (according to the same article as linked above). What do they make so different? Referring to unidimensional motion, it is obvious that it doesn't always make sense to write the speed as a function of position. Seems to me that this is a necessary condition to derive formulas like:  $$v^2=v_0 ^2 +2\int_{x_0}^{x}a\cdot dx$$  In fact, in the first step of the demonstration (the one I saw, but I think that this step is crucial) it's required to write $a=dv/dt=(dv/dx)(dx/dt)$, that doesn't make sense if $v$ isn't a function of $x$.   When can one rigorously write $v=v(x)$? What is an undefined reference/unresolved external symbol error and how do I fix it? I cannot make xmodmap run on login in Ubuntu 13.04. I have searched around, including in askubuntu and all answers I found do not work.  I have a file named .Xmodmap in my home folder which contains the desired mappings. If I run it manually it works fine, so there is no error there. In order to make it run on startup, I have tried:     Using various .xinitrc containing one of the following commands:      xmodmap .Xmodmap xmodmap ~/.Xmodmap   /usr/bin/xmodmap /home/NAME/.Xmodmap if [ -s ~/.Xmodmap ]; then xmodmap ~/.Xmodmap fi  Using .Xresources instead of .xinitrc with the same variations. Setting it as a startup application.   None of the above works in Ubuntu 13.04 (64-bit). I also saw a few ideas about globally changing the keyboard mappings, but most of them were not applicable in Ubuntu 13.04 (i.e. the corresponding files did not exist where specified) and I prefer not to touch the global settings anyway. How many and which are the uses of "const" in C++? As a novice C++ programmer there are some constructs that look still very obscure to me, one of these is const. You can use it in so many places and with so many different effects that is nearly impossible for a beginner to come out alive. Will some C++ guru explain once forever the various uses and whether and/or why not to use them? Reputation changes not visible in the achievement box (again) Just like , which was marked as . But today, it's not working again. I'm still notified of new badges:      Update: it looks like new events are now updated; reputation events from earlier this UTC afternoon are still missing: I have seen lots of UI designer nowadays including this kind of illustration i want to know the name of this style so that i can also learn and try this in my designs. Java - Method name collision in interface implementation I got a flat/puncture on my bike tube, how can I fix it myself without going to the nearest bike shop? What kind of equipment would I need? I upgraded from 16.04 to 18.04. When I press Ctrl+Alt+F3 I get the terminal which prompts for the username. When I type my username and press Enter, it doesn't wait for my password (its as if I pressed Enter without entering anything). Even if I enter something, the text shown in plaintext and then it keeps on saying my password is wrong. After few times, the screen is cleared and it prompts for my username again and the same loop goes on. In an hydrogen-like atoms the orbitals are solutions to the Schrodinger equation suitable for the problem.  They describe the regions where an electron can be found.  So, why don't they have spherical symmetric?  As in this picture:    Why, in a certain distance from the nucleus, are there points where an electron can be found, and points where it can't?  EDIT: Is there any intuation about the symmetry breaking?