Why is <? used for and which is the difference with <?php
Reference — What does this symbol mean in PHP?
My intuition tells me it's a trade off between speed and security, but how did the standardisation process select these three seemingly arbitrary key lengths (namely, AES-128, AES-192, AES-256). If a product of relatively prime integers is an $n$th power, then each is an $n$th power Show that if $n$, $a$, $b$, and $c$ are positive integers with $\gcd(a, b) = 1$ and $ab = c^n$, then there are positive integers $d$, and $e$ such that $a = d^n$ and $b = e^n$.   I know that (by Bezout) $\gcd\left(a,b\right) = 1$ implies $ax + by = 1$ for some integers $x$ and $y$, and also that $\gcd\left(a^n,b^n\right) = 1$, but this does not help me. I unplugged my USB stick from Ubuntu 16.04 without the save remove option, but exfat should be fine doing so. No read write was happening, the partition does not use journaling. What I end up with is an unmountable USB stick with checksum error.   What tools are there to recover the partition table or at least the data on the USB stick? What I am doing now is scanning via parted. Has anyone experienced the same problem with exfat and recovery options? Unfortunately parted probably won't detect the partition because .  I also tried to use Partition Wizard on Windows but it failed to detect anything, just showing unallocated space. How do I proceed? are there helpful tools under Windows or Ubuntu?    I also tried to use gpart -v /dev/sdb but it failed to detect anything. On OS X there is a tool called fsck_exfat, is there any on Windows?  update The disk is preinstalled with Parted Magic. After quick search no partition shows up. How to draw circle tangents and removing the inner lines? I'm new to Adobe Illustrator and I wanted to accomplish this task. How do I remove the inner lines in my drawings? I tried with all the pathfinders effect but it keeps removing my tangent lines (the lines connecting both my circles).    It works like a charm as I followed the selected's answer guide:  Here it is. using $$ in a post causes strange number series to appear Let $R$ be a ring (unital, not necessarily commutative), $M$ a finitely presented left $R$ module. Suppose $m_1,\ldots,m_n\in M$ generate $M$. This determines a surjection $f:R^n\to M$.     Must the kernel of $f$ be finitely generated?   This is true by definition if the generating set $m_1,\ldots,m_n$ is the one coming from the finite presentation of $M$. Not sure this is something which people will know on here are not.    We currently have a BI setup where we have Integration services on one SQL instance and the data warehouse database on a separate SQL Instance.    My question is, as no users physically connect to the Integration services SQL instance and it is purely used to execute package from the integrations service catalog via SQL agent, do we need to License every user i.e. Cal's for that SQL instance.  Basically i'm wanting to know if I could utilize SQL 2016 for an integration services instance and use features like Json manipulation etc and then load this data into the 2014 version instance...but what level of licensing will I need? .NET Attributes: Why does GetCustomAttributes() make a new attribute instance every time? So I was playing around a little more with attributes in .NET, and realized that every call to Type.GetCustomAttributes() creates a new instance of my attribute. Why is that? I would think that the attribute instance would basically be a singleton-per-MemberInfo, with 1 instance bound to the Type, PropertyInfo, etc...  Here is my test code:  using System;  namespace AttribTest { [AttributeUsage(AttributeTargets.Class)] class MyAttribAttribute : Attribute {     public string Value { get; set; }      public MyAttribAttribute()         : base()     {         Console.WriteLine("Created MyAttrib instance");     } }  [MyAttrib(Value = "SetOnClass")] class MyClass { }  class Program {     static void Main(string[] args)     {         Console.WriteLine("Getting attributes for MyClass.");         object[] a = typeof(MyClass).GetCustomAttributes(false);         ((MyAttribAttribute)a[0]).Value = "a1";          Console.WriteLine("Getting attributes for MyClass.");         a = typeof(MyClass).GetCustomAttributes(false);         Console.WriteLine(((MyAttribAttribute)a[0]).Value);          Console.ReadKey();     } } }   Now if I were to implement attributes, I would expect the output to be:  Created MyAttrib instance Getting attributes for MyClass. Getting attributes for MyClass. a1   Where the "class loader" (sorry, I have more of a Java background, not 100% sure how .net loads its types) would compile MyClass, and create an instance of MyAttribAttribute, and store them together somewhere. (probably the Perm Gen in the heap if this were Java) The 2 calls to GetCustomAttributes() would then just return the same earlier created instance.  But the actual output is:  Getting attributes for MyClass. Created MyAttrib instance Getting attributes for MyClass. Created MyAttrib instance SetOnClass   So... why? It seems like creating a new instance of all these objects for every call is a bit excessive, and not good for performance/memory management.  Is there any way to always get the same instance over and over?  Anyone have any ideas why it was designed this way?  The reason I care at all is because I made a custom attribute that internally holds some validation information, so in the Attribute I basically have a "private bool Validated" that I set to true. The validation stuff takes a while, so I don't want to run it every time. Now the problem is that since it creates a new instance of the attribute each time I get the attributes, Validated is always "false". Comment authors are not getting migrated Find and remove large files that are open but have been deleted How does one find large files that have been deleted but are still open in an application? How can one remove such a file, even though a process has it open?  The situation is that we are running a process that is filling up a log file at a terrific rate. I know the reason, and I can fix it. Until then, I would like to rm or empty the log file without shutting down the process.   Simply doing rm output.log removes only references to the file, but it continues to occupy space on disk until the process is terminated. Worse: after rming I now have no way to find where the file is or how big it is! Is there any way to find the file, and possibly empty it, even though it is still open in another process?  I specifically refer to Linux-based operating systems such as Debian or RHEL. What is the purpose of a serial number? How to add keyboard shortcuts? To prevent overfitting people people add a regularization term (proportional to the squared sum of the parameters of the model) with a regularization parameter $\lambda$ to the cost function of linear regression. Is this parameter $\lambda$ the same as a lagrange multiplier? So is regularization the same as the method of lagrange multiplier? Or how are these methods connected? Why isn't $\mathbb Z [\sqrt{pq}]$ a factorial domain This is exercise 8 on page 147 of Jacobson's Basic Algebra:     Let $p$ be a prime of the form $4n+1$ and let $q$ be a prime such that $ \left( \frac{q}{p} \right) =-1$. Show that $\mathbb Z[\sqrt{pq}]$ is not factorial.   Here, $ \left( \frac{q}{p} \right) =-1$ means that $\overline{q}$ is not a quadratic number in the field $\mathbb Z / (p)$.  In the special case when $p=5$ and $q=2$, $9 = 3 \cdot 3 = (\sqrt{10} +1 )(\sqrt{10 }-1)$, with $3$ and $\sqrt{10} +1$ or $\sqrt{10} - 1$ nonassociates. But I have no idea what can I do with the general case.  I know that primes of the form $4n+1$ can be written in the form $m^2 + n^2$ with $m,n \in \mathbb Z$. But when $q$ is odd and not of the form $4n+1$, $pq$ is not the sum of two quadratic numbers. How can I use the fact $\left( \frac{q}{p} \right) =-1$?  Thanks~ Is there a filesystem that is "friendly" to both windows and Linux? I need to draw a tree, and constantly using dotty and including the PNGs is starting to be a pain. Is there a way to get LaTeX to draw it's own trees that doesn't involve learning an entirely new language like TikZ? A case of optional “that”: “check the” vs. “check that the” Consider the following use case:   Please check the username and password are correct. Please check that the username and password are correct.   In this case, I would say that that is required because it feels more natural to me and so the flow is better. However, is the lack of that wrong in this case?  The question boils down to: when is that optional? See . A quick summary:   That is optional if the pronoun is the object. That is required if the pronoun is the subject.   I think that we fall into the second case: that is required because the relative pronoun is the subject. But I'm not sure if I'm interpreting these rules correctly. Can someone please advise? What does A a() mean? MySQL Replication : 1 Slave / Multiple Masters How do you evaluate this integral $\int \frac{6x^{3}+7x^2-12x+1}{\sqrt{x^2+4x+6}}dx$ $$\int \frac{6x^{3}+7x^2-12x+1}{\sqrt{x^2+4x+6}}dx$$  I have met this complex integral today, how do you evaluate this? Can you do this in more steps?  Is this an elliptic integral? I don't know how to evaluate this integral at all.