i'm pretty confused with how PHP works, i'm using PHP7.3 and i made a webshell running as www-data. And the shell.php is of another owner, so www-data can executes the file as "other". The file doesn't have x permission, so how can PHP execute that with just read permission? Thanks for helping me.    PHP file:  &lt;?php system('whoami; id'); ?&gt;
I can seem to run scripts (.sh) with and without them being set as executable. So where exactly this matters?
Why is the ROC curve two-dimensional instead of three-dimensional? Every retraction is a quotient map? I have to proof that every retraction is a quotient map.. I have no idea where to start or what to use! A retraction $r:X \rightarrow A$  is a continuous map s.t. $r(a)=a$ for every $a\in A$. Why did R.A.B. put the locket back in the basin? led me to asking this one. R.A.B. takes the "real" locket out and asks Kreacher to destroy it, then puts the "fake" locket back in the basin. Why would he feel the need to do this? He knows already that Voldemort has used someone else to drink the potion (Kreacher). In fact Kreacher's story to him about his mistreatment on the island seems to push him over the edge to act.   Instead of assuring that someone else (most likely innocent like Kreacher) would have to drink from the basin, why not just leave the note outside the basin for someone to find? If Voldemort finds it then so be it, at least then no presumably innocent person would have to drink again. I had always kind of wondered why we didn't see interference in things like windows -- we were taught that the condition is that the thickness of the film/slab/medium just has to be an integral number of wavelengths, $d=m\lambda$. My logic was, if visible light has wavelengths ~400-780nm, any window pane has got to be an integral number of wavelengths (or close to integral) for some of the wavelengths in the visible.  For example, if a window is, $6mm = 6\times10^6nm$ thick, then you should see interference for wavelengths (and some range around them) 200nm, 250nm, 300nm, 400nm, 500nm, 600nm... Because 6mm is an integral number of each of those.  Obviously that would be really annoying and isn't the case. I found  (warning: PDF) source that seems to explain it and I was wondering if what they're saying is sound. On the 10th page (p171 for them), it says that the reason we don't see this interference is that no window is that smooth, it has a variance in the thickness of at least several wavelengths, so the interference effect is effectively average out among all those thicknesses, which usually gets rid of it. They do the math and show that.  Is that the reason?  If so, that leads me to two questions: Could we, if we were really careful and used something like MBE, make a glass window with that sort of accuracy, and then see interference effects in the optical range? I know that quartz crystal monitors can easily give you nanometer accuracy for evaporators and sputterers, but they also have pretty limited growth rates.  My second question is, then, do we see interference effects in glass windows with electromagnetic radiation of a comparable wavelength, like microwaves?  Thanks! I have a data frame in python where I need to find all categorical variables. Checking the type of the column doesn't always work because int type can also be categorical.   So I seek help in finding the right hypothesis test method to identify if a column is categorical or not.   I was trying below chi-square test but I am not sure if this is good enough  import numpy as np data = np.random.randint(0,5,100) import scipy.stats as ss ss.chisquare(data)   Please advise. If a matrix has orthonormal columns, they must be linearly independent, so $A^+ = (A^T A)^{−1} A^T$ . Also, the fact that its columns are orthonormal gives $A^T A = I$. Therefore,  $$A^+ = (A^T A)^{−1} A^T = (I)^{-1}A^T = A^T$$  Thus, $A^+ = A^T$. Am I correct? Thank you. dividing a string array in groups Sci-fi film about terraforming Venus, inadvertently killing the native worm-like Venusians I have been searching for the name of a short sci-fi film for decades.  The story is about a team of scientists who figured out a way to terraform Venus by sending algae plants there in a rocket which changes the atmosphere so that humans can live there.  At the end, it works, but the first people that arrive on Venus discover that the algae has killed the native Venusians, a race of worm-like creatures.  The final shot (as I remember it) is of an astronaut finding a half-sphere with writing on it, and he says “it wasn't much, but it showed that they were intelligent…”  I saw it on TV in probably the late seventies or early eighties, possible as an HBO short take that they would show to fill time in between movies.  Does this sound familiar to anyone? Compound possessives and yours That's basically the question, is there a "right" way to implement operator&lt;&lt; ? Reading  I can see that something like:  friend bool operator&lt;&lt;(obj const&amp; lhs, obj const&amp; rhs);   is preferred to something like   ostream&amp; operator&lt;&lt;(obj const&amp; rhs);   But I can't quite see why should I use one or the other.  My personal case is:  friend ostream &amp; operator&lt;&lt;(ostream &amp;os, const Paragraph&amp; p) {     return os &lt;&lt; p.to_str(); }   But I could probably do:  ostream &amp; operator&lt;&lt;(ostream &amp;os) {     return os &lt;&lt; paragraph; }   What rationale should I base this decision on?  Note:   Paragraph::to_str = (return paragraph)    where paragraph's a string. I would like to treat a user as a non-gender noun and refer to it with the gender-neutral pronoun, it. E.g.,     The user defines two variables, x and y. It then multiplies each variable by a prime number.    However, on  I found this:      The word "it", however, has an extremely impersonal connotation, even offensive, in common usage and is rarely used in English to refer to an unspecified human being or person of unknown gender. This is because the word "it" connotes that the person being specified is inferior to a person or is an object.   Is to appropriate to refer to a person of unknown sex as it?  Should I rephrase my sentence as follows:     The user defines two variables, x and y. The user then multiplies each variable by a prime number. Java generics T vs Object Is there a set of lines in $\mathbb{R}^3$ such that their union is equal to the set of points with not all coordinates rational? Does there exist a set L of pairwise disjoint lines, each line in an axis direction, in $\mathbb{R}^3$ such that their union is equal equal to $\{ x : x \text{ has at least one irrational coordinate}\}$? Is it possible record videos of my screen? Suppose that I would like to record some video sessions of Angry Birds on my phone.   Are there any apps that I can use? I have root permissions. Example of a finite non-commutative ring without a unity Give an example of a finite, non-commutative ring, which does not have a unity.    I can't think of any thing which fits this question. I was thinking $M_2(\mathbb{R})$ but it has the identity. Any help is appreciated. Does casting blindness on a Medusa (or other gaze using creature) stop their gaze attack? I just wanted to ask whether there is any command which would work on common shells (bash, dash, kornshell)? It is supposed to check if the line variable contains any part of the path.  if [[ $line =~ "$PWD"$ ]] ;then Do small title edits constitute trivial edits? Cross-referencing problem if counter of theorem-like environments is shared The problem is when i share numbering the \cref can't show name, even by \crefname and \autoref show all name Equation.  Here is an MWE:  %&amp;latex \documentclass{amsart}  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % If you want to insert other packages. Insert them here \usepackage{amsthm} \usepackage{hyperref} \usepackage[nameinlink]{cleveref} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  \begin{document}  \numberwithin{equation}{section}  \newtheorem{The}[equation]{Theorem} \crefname{The}{Theorem}{Theorems}  \newtheorem{Dfn}[equation]{Definition} \newtheorem{Lem}[equation]{Lemma} \newtheorem{Prs}[equation]{Proposition} \newtheorem{Crl}[equation]{Corollary} \newtheorem{Rmk}[equation]{Remark}  \begin{The}\label{T1}    Assume ... \end{The}  ... \begin{Dfn}\label{D1}    Assume ... \end{Dfn}  ... \begin{Lem}\label{L1}    Assume ... \end{Lem}  ... \begin{Prs}\label{P1}    Assume ... \end{Prs}  ... \begin{Crl}\label{C1}    Assume ... \end{Crl}  ... \begin{Rmk}\label{R1}    Assume ... \end{Rmk}  \begin{equation}\label{E1}    Assume ... \bigskip \end{equation}  \noindent \cref{T1} \\ \cref{D1} \\ \cref{L1} \\ \cref{P1} \\ \cref{C1} \\ \cref{R1} \\ \cref{E1} \\  \noindent \autoref{T1} \\ \autoref{D1} \\ \autoref{L1} \\ \autoref{P1} \\ \autoref{C1} \\ \autoref{R1} \\ \autoref{E1} \\  \end{document}     How can I solve it? Is it possible to copy an object in Illustrator so that if you make a change in any of them the changes will apply in both? Actually I have this situation where I have a lot of instances of the same object and I need to be faster on changes and copy-ing again and again is not a proper solution, but consumes a lot fo time.  Thank you for your time!