Found this technique to verify if the email address is in correct form of not.  function check_email($email) {           if( (preg_match('/(@.*@)|(\.\.)|(@\.)|(\.@)|(^\.)/', $email)) ||              (preg_match('/^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/',$email)) ) {               return true;         } else {              return false;         }            }   I Am a newbie in php. What this big regex commands mean?
I don't really understand regular expressions.  Can you explain them to me in an easy-to-follow manner?  If there are any online tools or books, could you also link to them?
Clone Method not working I am trying to Clone a lead when certain condition is arrived using before trigger but i am not able to see cloned record.   for( Lead ld : Trigger.new ) {                          if(ld.Integration_Source__c == 'Hubspot' &amp;&amp; Trigger.isUpdate){         Lead LeadBeforeUpd = Trigger.oldMap.get( ld.Id );         if(ld.Program__c != LeadBeforeUpd.Program__c ){            Lead ClonedLead = new Lead();            ClonedLead = LeadBeforeUpd.clone(false, false, false, false);         }     }  } Force ssh to not print "Remote host identification has changed" warning Is there a way to avoid ssh printing warning messages like this?   @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@   Although the remote host identity has changed but I know it is fine and  just want to get rid of this warning. Confusing article status for journals of American Mathematical Society: "reviewing" AND "being handled by an editor" The web page of my article in the AMS editorial system for some three months says &quot;Article status: Reviewing&quot; and in the next line &quot;Your paper is being handled by an editor&quot;. I find this confusing as the &quot;reviewing&quot; status appears to suggest that the article is with the referee(s) rather than with the editor but this in turn seems to contradict the line &quot;Your paper is being handled by an editor&quot;.  Could someone with enough experience with AMS journals please explain how should one interpret the combination of &quot;Article status: Reviewing&quot; and the line &quot;Your paper is being handled by an editor&quot; at the article page? More broadly, which are the possible article statuses in the AMS editorial system?  Many thanks in advance. How to ignore the first line of data when processing CSV data? What is the correct way to use infinitive after the verb "help": with or without "to"? What is the correct way to use infinitive after the verb "help": with or without "to"?  For example:     Please, help me to understand this.   or:     Please, help me understand this. Identifying a resistor with a weird band combination Re-number a list when a new entry is inserted Programmatically disable apt unattended upgrades How can I programmatically/script disable apt unattended upgrades? Running Ubuntu 16.04. glob() - sort array of files by last modified datetime stamp What command(s) would you use to extract all of the usernames from a database called /etc/passwd and then sort this output alphabetically in reverse order? Laplace equation of composite function Suppose we have $f(x,y)$, which satisfies Laplaces equation: $\frac{\delta^2f}{\delta x^2}+\frac{\delta^2f}{\delta y^2}=0$  Does $f(\frac{x}{x^2+y^2},\frac{y}{x^2+y^2})$ also satisfy Laplace equation? I would like to create a minecraft server for me and and my boyfriend to play on.  How do I set it up? Do I need any additional software? Do you have some links to walkthroughs or tutorials?  I have tried to set this up a few times but have failed every time. From the limit definition of differentiability, determine where the function $f(x) = \sqrt{x}$ is differentiable? For the function $f(x) = \sqrt{x}, \hspace{2 mm} f: [0, \infty) \rightarrow \mathbb{R}$, I wish to find all points $a$ at which $f(x)$ is differentiable, from the definition $$ f'(x) = \lim_{x \rightarrow a}\frac{f(x)-f(a)}{x-a} $$  Clearly, for our function $f(x) = \sqrt{x}$, this gives us $$ f'(x) = \lim_{x\to a}\frac{\sqrt{x} - \sqrt{a}}{x-a} $$  So the question boils down to showing for what values of $a$ this limit exists. How would this be done? Intuitively, I know that the answer is that the limit exists for all $a \in [0, \infty)$ and is given by $\frac{1}{2 \sqrt{a}}$, but I'm unsure of how to prove this from the limit definition of differentiability. How do you calculate the probability density function of the maximum of a sample of IID uniform random variables? Given the random variable  $$Y = \max(X_1, X_2, \ldots, X_n)$$  where $X_i$ are IID uniform variables, how do I calculate the PDF of $Y$? Virtualbox Windows 10 Guest installation is freezing up in 14.04 I've installed VirtualBox using the Software Centre and I'm running a system on Ubuntu 14.04 with 8gb RAM, 64-bit dual core processor.  I want to run Windows 10, I've tried both 64 and 32 bit versions, in virtualbox. However, every time I start up windows 10 it gets to the point where the dots go round in a circle, then it freezes up and crashes back to the virtualbox manager. The only information it gives me is that the virtual machine was aborted.  I've changed the settings around a lot and nothing is working.  Any help would be appreciated.  Oh, and I've run Windows 10 technical preview on this machine before, a while ago  Thanks for any help in advance. What's that ship in the opening credits of 'Star Trek: Enterprise'? How to search based on part of file name in Google Drive I'd like to be able to find all files in my Google drive that contain the string "_INSTRUCTION_" in the file name. Is there a way to do this?  EDIT 1: When I search for "RMA2013", I should get a dropdown with several options. As you can see, there are several Word and .pdf files with the phrase "RMA2013". Still I get no dropdown help:   And even if I click the search button, I get nothing: Joining lots of small polygons to form larger polygon using PostGIS? Target filesystem doesn't have requested /sbin/init We all know that $\sqrt[3]{3}\not\in \mathbb{Q}({\sqrt[3]{2}})$ intuitively. We even know that $\sqrt[3]{p}\not\in \mathbb{Q}(\sqrt[3]{q})$ for two distinct primes $p, q$. However, I don't know how to prove these things rigorously. In case of $\sqrt{p}\not\in \mathbb{Q}(\sqrt{q})$, we can just set assume $\sqrt{p}=a+b\sqrt{q}$ for some $a, b\in\mathbb{Q}$ and deduce a contradiction. However, in cubic case, expansion of $(a+b\sqrt[3]{2}+c\sqrt[3]{4})^{3}$ is very complicated and even I expand this I couldn't get any contradiction by this.  To be specific, it gives us 3 diophantine equations  $$a^{3}+2b^{3}+4c^{3}+12abc=3$$ $$a^{2}b+2b^{2}c+2c^{2}a=0$$ $$ab^{2}+2bc^{2}+ca^{2}=0$$  and I don't know how to check solvability of this kind of diophantine equations (over $\mathbb{Q}$). Even if there exists a way to check solvability, I cannot convince that it can be used to prove $\sqrt[3]{p}\not\in \mathbb{Q}(\sqrt[3]{q})$.   So I tried to use Galois theory, but actually I don't know where to go. I assumed $\mathbb{Q}(\sqrt[3]{3})=\mathbb{Q}(\sqrt[3]{2})$ and take a Galois closure, i.e. $K=\mathbb{Q}(\sqrt[3]{3}, w)=\mathbb{Q}(\sqrt[3]{2}, w)$ where $w^{3}=1$ then tried to use field norm maps. We can check that $\beta=\sqrt[3]{3}\cdot\sigma(\sqrt[3]{3})\cdot\sigma^{2}(\sqrt[3]{3})\in \mathbb{Q}$ when $\sigma\in Gal(K/\mathbb{Q}), \sigma(\sqrt[3]{2})=\sqrt[3]{2}, \sigma(w)=w^{2}$. But I cannot get any information from this.   Edit : It would be great if there is a simple algorithm to check whether $\alpha\in K$ or not for a given algebraic number $\alpha$ and a number field $K$.