We have equivalent symbol \equiv, but how to write unequivalent like this
I know what my symbol or character looks like, but I don't know what the command is or which math alphabet it came from. How do I go about finding this out?
Is it possible to redirect a command's output to cd? For example, I searched for a directory using locate and got the path to it. Now, instead of writing a cd path, can I redirect the locate output to cd?  I tried this:  $ locate Descargas | grep Descargas$ /home/oliver/Descargas $ locate Descargas | grep Descargas$ | cd $ locate Descargas | grep Descargas$ &gt; cd $ locate Descargas | grep Descargas$ &lt; cd /home/oliver/Descargas $    No luck. This probably isn't particularly useful, but I'm curious. If statement evaluating true no matter what. Python 3.3.0 Why does the connection time out when connecting to a server? Why does the reputation need to be publicly displayed? Possible Duplicate:          The idea of getting greater privileges with greater reputation is good, but what is the benefit of publicly displaying that reputation? Since SO claims to be about good questions and answers, that purpose is better served if the reputation is only visible to the account owner (and, of course, the site admins). This would better ensure that content gets pushed up solely by its merit, and not based on the author. (See )   Edit (copied from comment to an answer below): Once you have gathered high reputation, you can also gather more reputation with ordinary answers, especially from newbies (newbies on the topic, not on the site) who usually choose to accept or upvote an answer on the assumption that "since a high-rep user has posted it, it is probably right". Can you guarantee that doesn't happen often? Touch enabled monitors and Android Mean Time to Failure (MTTF): When disk manufacturers post this, how should you interpret their numbers? Mean Time to Failure (MTTF) is usually given in terms of hours, and by doing some calculations, it seems that a disk should fail only after a good number of years have gone by.  It seems that disks need repair more often than that. Does anyone know why this is so?  I figured that there is something fishy about this metric. Am interpreting something wrong here? I am reading Introduction to Quantum Computing by Kaye, Laflamme, and Mosca. As an exercise, they write  "Prove that if the operators $P_{i}$ satisfy $P_{i}^{*}=P_{i}$ and $P_{i}^{2}=P_{i}$ , then $P_{i}P_{j}=0$ for $i\ne j$.''   In the context of this problem, it has been assumed that $I=\sum_{i=1}^{n} P_{i}$, where I suppose that $n$ could be infinite. I have shown that this is true in the trivial case $n=2$, but the general case has been eluding me. How should I attack this? How to use resistors? I have a power supply of 5 volts @ 1A. I want to reduce the current from 1A to 250mA. Which resistor should be use?   I tried this equation(Ohm's Law):  R = V / I  = 5/(0.75)  = 6.66 Ohms.  I tried the 6.66 Ohm resistor but it only reduce few mili Amps. Geometric series and big theta Consider the following function:  $$S(n)=1+ c + c^2 + ··· + c^n,$$  where c is a positive real number.  (A) This function is the sum of a geometric series. Give a precise closed-form formula for $S(n)$, interms of $c$ and $n$, in the case where $c \neq 1$.  (B) Show that $S(n)$  is:  $\theta(1)$ if $c&lt;1$  $ \theta(n)$ if $c=1$  $\theta(c^n)$ if $c&gt;1$    can someone please explain how i can go about finding the solutions for these problems, i have never encountered these and am stuck, i know that big theta means that the function is bond on both sides but how do i got about finding the answer?  (edit) im still having trouble understanding part B. can someone please explain? (can someone walk me through the second one) so far i have $n \leq c^{n+1} \leq ???$  (edit #2) i tried doing the first one can someone verify if i did it right  $S(n)$ is $\Theta(1)$ if c&lt;1  (1)$S(n)$ is $O(1)$ if c&lt;1  (2)$S(n)$ is $\Omega(1)$ if c&lt;1  (1) $$\frac{C^{n+1}-1}{C-1} \lt (C_1)(1)$$ $$\frac{C^{n+1}-1}{C-1} \lt (C_1)$$ $$C^{n+1} \lt C_1(C-1)$$ $$C^nC-1 \lt C_2C-1$$ $$C^n \lt C_2$$ $$C^n \lt 1$$ since c&lt;1 this means that any number that will be $C^n$ will be less then 1 for all positive n  i did the omega part pretty much the same way and got $$C^n \gt C_2$$ $$C^n \gt 0$$ since c&lt;1, $C^n$ can potentially become very very small so the only thing bounding it is 0 for all positive n If nonempty, nonsingleton $Y$ is a proper convex subset of a simply ordered set $X$, then $Y$ is ray or interval? This is from Exercise 7 in p. 92 in Munkres's Topology.  Except for the trivial cases such as $Y$ is empty set or singleton, it seems if $Y$ is convex in an simply ordered set $X$ then $Y$ is interval or ray.  But I cannot start my proof because I cannot use $\sup$ or $\max$ functions.  What should I do? How do you round a number to two decimal places in C#? How to install hp scanjet 200 in Ubuntu 12.04? Unable to scan with hp scan-jet 200. When I type lsusb command in terminal it shows the scanner details.  I opened the simple scan which displays no scanners found, and x sane image scanners also displays the same error. Subset of a finite set is finite We define $A$ to be a finite set if there is a bijection between $A$ and a set of the form $\{0,\ldots,n-1\}$ for some $n\in\mathbb N$.  How can we prove that a subset of a finite set is finite? It is of course sufficient to show that for a subset of $\{0,\ldots,n-1\}$. But how do I do that? Can prematurely powering down a computer cause bad sectors in a hard drive? Q1: Can forcibly powering off a PC without using the built-in shutdown/reboot functions, cause a HDD to accumulate bad sectors? Whether it be the result of BSODs, lockups, crashes, etc.   Q2: If so, are these bad sectors repairable? I know an OS typically relocate bad sectors to other areas of the drive, but once a drive accumulates too many it just dies.   I have read up and saw things about 'soft' and 'hard' bad sectors. One caused by software and the other being actual physical damage. The reason I am asking this is because I have had several HDDs die on me in the past year, far before their estimated lifespan, and one thing they all had in common was that I had forcibly powered off my PC a lot. Why is it considered so dangerous to travel in South Africa? As, the above link shows, other countries have similar murder rates but they are not in the radar of international travelers.  For example, as seen in the list, Puerto Rico has similar statistics. But, personally, I never heard of Puerto Rico to be a dangerous place to travel.  Why is it considered so dangerous to travel in South Africa? Is that due to the incompetent law enforcement agencies? Can someone show me a straightforward proof that  $\lim_{m\to\infty}(1+\frac{r}{m})^{mt}=e^{rt}$  Thanks! I understand test -n &lt;expression&gt; to return false if the expression evaluates to a string length of greater than 0.  Why then does the following happen?  Macbook:~ echo ${#undeclared_variable} 0 Macbook:~ test -n $undeclared_variable &amp;&amp; echo Foo Foo   Bash 4.x  My expectation is that since test -n $undeclared_variable should evaluate false, that Foo should not be echoed.  If I use [[  ]] instead of test, it works as expected. How to get next/previous record in MySQL? How to modify existing, unpushed commit messages? I wrote the wrong thing in a commit message.  How can I change the message? The commit has not been pushed yet. Why is $1$ not considered a prime number?  Or, why is the definition of prime numbers given for integers greater than $1$?