Doubts of security: Mysqli vs PDO
mysqli or PDO - what are the pros and cons?
This is a homework question of mine that Ive answered and I'd really like some feedback on my solution.       Prove or find a counter example to the claim that for all sets $A,B,C$, $$\text{if  }A\cap B=B\cap C=A\cap C=\emptyset \text{ then } A\cap B\cap C\neq \emptyset$$.   Since I can only either prove it is true, OR find a counter example I have gone with the latter because I think this statement is not true. My counter example is as follows:  Let $A = \{1,2,3 \}$ , $B = \{4,5,6 \}$ and $C = \{7,8,9 \}$. It is then clear that $A ∩ B =  B ∩ C =  A ∩ C = \emptyset$ .  If we let $x ∈ A\cap B\cap C$ then $x$ must be in $A$ and $B$ and $C$. Since this cannot be possible because there are no common elements then this implies that $A∩B∩C$ has to be equal to a null set i.e $A∩B∩C = \emptyset$ and thereby showing that (at least for this scenario) if $A \cap  B =  B \cap  C =  A \cap  C = \emptyset$ then $A\cap B\cap C = \emptyset$.  Is this okay? Any feedback will be greatly appreciated thank you! How do I get evolution items like King's Rock? Frequency count of two column in R Formula Error: Syntax error. Extra ',' I am trying to write a formula for opportunities but I keep getting the following error   Error: Syntax error. Extra ','  Here is my formula       IF      (TODAY() &gt; CloseDate &amp;&amp; TEXT(StageName)='Donation Likely')     ||      (TODAY() &gt; CloseDate &amp;&amp; TEXT(StageName)='Donation Prospecting'),"Past                   Due","Expecting") Python does not find packages installed without Anaconda I'm trying to install kivy for python 3 using apt-get:      sudo apt-get install python3-kivy   And it is installed in      /usr/lib/python3/dist-packages   But, when I tried to load it in python, I get a ModuleNotFoundError      Python 3.6.3 |Anaconda custom (64-bit)| (default, Oct 13 2017, 12:02:49)      [GCC 7.2.0] on linux     Type "help", "copyright", "credits" or "license" for more information.     &gt;&gt;&gt; import kivy     Traceback (most recent call last):       File "&lt;stdin&gt;", line 1, in &lt;module&gt;     ModuleNotFoundError: No module named 'kivy'   When I check the system path from python, I only get packages in Anaconda:      &gt;&gt;&gt; import sys     &gt;&gt;&gt; print('\n'.join(sys.path))      /home/santiago/anaconda3/lib/python36.zip     /home/santiago/anaconda3/lib/python3.6     /home/santiago/anaconda3/lib/python3.6/lib-dynload     /home/santiago/anaconda3/lib/python3.6/site-packages     /home/santiago/anaconda3/lib/python3.6/site-packages/torchvision-0.2.0-py3.6.egg   Is there any way to include the '/usr/lib/python3' path to Anaconda?  Thanks. Why is the multiplicative group of a finite field cyclic? Why is the multiplicative group $(K\smallsetminus\{0\},\cdot)$ of a finite field $(K,+,\cdot)$ always cyclic? How do I insert a backslash inside a mathematical statement? I'm trying to write a set subtraction operation in an AMS formatted template.  In the end, what I want should look like A\B.  But I'm doing this in math-mode $A\B$ and this gives me errors.  I've also tried using the \diagdown symbol, but it doesn't work either.  Is there another way to do this? Why is the main page showing only the user login form? Do downvotes on Meta truly mean something different? It is often said that voting on Meta means something different than voting on regular sites. Upvotes mean "I agree", and downvotes mean "I disagree".  However, I submit that this is not the case. Downvoting of a question has one effect in particular: censorship.  Once a question reaches -8 votes, it disappears from the front page. It can still be found; it isn't deleted. But all it takes is a net 8 downvotes for a question to be more or less lost without a direct link.  You might say that a net 8 downvotes obviously means that the community doesn't agree or want that. Well... does it? Particularly on polarizing issues, a question can temporarily get -8 votes as different people come online and see it. Maybe certain people with a certain belief all see it at once and downvote it a lot.  The front page is how most people find stuff they want to talk about, vote on, or answer. Removal from the front page means that most people will not find it without being pointed directly to it. Once a question hits -8, it is unlikely to be upvoted again. Edits will be irrelevant, new answers won't matter. The question is basically exiled.  The problem is that, on polarized topics, fast mass downvoting can quash any idea that is not popular with the most active members. After all, the most active members are the ones who are most likely to be online and see it. If a bunch of MSO regulars see it and downvote it, it goes away. Someone who checks MSO maybe once a day is less likely to be able to catch the question before it is exiled. This gives undue power to members who are most active on MSO, simply because they have more free time to spend on MSO.  I think this is a significant problem for polarized topics. It becomes very difficult to adequately discuss something that a significant number of active members dislike, even if the community at large doesn't mind.  Consider . It currently stands at +9/-8. Initially, in the first few hours, the question was heavily downvoted and even closed. However, after a day, it was upvoted and reopened.  This shows that a question can initially have a negative response, but later get a positive one. And you can check; any edits I did to the question were relatively minor. The question posted as is was initially negative, but ultimately positive.   If that -8 happened to all come first, odds are good that the +9 and the reopen would never have happened. Those 9 people would never have had the chance to weigh in on the subject. And that's wrong.  It is wrong for someone's potential vote to not matter just because they don't visit MSO multiple times in a day. It is wrong for someone's potential vote to not matter just because they have a different sleep schedule from many of MSO's members.  The problem is one of timing. Heavy dislike from active members who quickly see the question and downvote it can kill a question before someone who might upvote it ever even sees it.  I suppose the best suggestion would be to either lower the -8 threshold (or remove it altogether) or keep it from kicking in until 1-2 days has passed. If the question isn't active, it'll already be off the front page. And if it is active, then enough people will have seen it to know if the threshold represents a real consensus or just the fast-acting few. Comma with 'who' in this specific sentence Can you shed light into this?  The coach came to the defence of the player who has been sacked from the team following his differences with the captain.  OR  The coach came to the defence of the player, who has been sacked from the team following his differences with the captain.  Isn't the subordinate clause that begins with 'who', non-restrictive? Are there irreducible polynomials that are partially solvable by radicals? In general, polynomials of degree 5 or higher, with rational coefficients, are not solvable by radicals. There are some exceptions and trivial cases, for example $x^5-5x+12$ and $x^{100}+x^{25}+3$, respectively.  All irreducible polynomials with rational coefficients, that I am aware of, have either none or all roots that can be expressed by radicals.  Do partially-solvable irreducible polynomials exist? If they do, are there any examples known?  I mean, for example, an irreducible polynomial of $n$th degree that can be split over $Q(\sqrt{2})$ into two polynomials of 3rd and $(n-3)$th degrees, where the polynomial of $(n-3)$th is not solvable by radicals.    At  Alexander Gruber wrote:     Polynomials which are not solvable by radicals have (at least one) root that cannot be written by any combination of the operations of addition, multiplication, and the taking of nth roots.   I am not sure if he meant only reducible polynomials, and/or with non-rational coefficients, as polynomials that have "at least one" root that cannot be expressed by radicals. Copy over ssh and execute commands in one session B2B application: users has its own users B2B Scenario I am trying is that:  The following Roles exists in the system:  Super Admin Super Admin Staff Owner (client) Admin (owner i.e. client and creates admin to define sales counters) Sales Counters  That means there are users who'll create their own sub users e.g.  [FLAG-A] ROLE &quot;SUPER ADMIN&quot; creates a ROLE &quot;Owner&quot; and &quot;OWNER&quot; creates its own sub users ROLES i.e. &quot;ADMN&quot; &amp; &quot;SALES COUNTER&quot;. Each role obviously has its info to login to the system I tried to design database as following:  In this diagram I am assuming that main user creates sub user that in my view many to many relationship so I have to add table between them as &quot;USER_PERSON&quot;. Problem is to set &quot;WHO CREATED USER&quot; in the system. I mean which user has created sub user as described in [FLAG-A]  Please check this diagram What is the best word describing the nature of expiring in a short amount of time, connoting "losing public attention"? 408 Request Time-outs still continues I'm frequently getting 408 Request Time-out errors  when browsing through Stack Overflow and Meta. I used to get this four or five times a day before, but now it has become very frequent. I've read  in which Kyle Brandt ♦ says:     We send our web logs to SQL so we can query them. It turns out that we have a bug that prevents 408s from being logged to SQL. [...] I will do more extensive research when our 408s are part of queryable logs (should be a week or two [...]).   My internet connection is somewhat stable and I haven't experienced this issue on other sites before. I don't think it's a browser-specific issue as it is reproducible on latest versions of Google Chrome and Firefox (on Ubuntu 13.10). However, it is specific to Stack Overflow and Meta. I'm unable to reproduce this on other SE sites.  Am I the only one facing this issue? Could it be something wrong with the regional CDN or something like that? Could someone please take a look at this issue? ()  This appears when I try to close-vote questions, too: Forced to Quit PhD although the hard and proved work Showing a set is closed under inverses Let $G$ be a finite group, say a group with $n$ elements, and let $\emptyset \neq S \subseteq G$. Suppose $e \in S$, and that $S$ is closed with respect to multiplication. Prove that $S$ is a subgroup of $G$.    Let $G = \{a_1, \ldots, a_n\}.$ Let $a_i \in G.$ Then any number of $a_ia_1, a_ia_2, \ldots, a_ia_n \in S,$ since $S$ is closed under multiplication. One of those $a_ia_j$ is $e$ since $e \in S.$ Then either $a_i$ or $a_j$ is $a^{-1}.$ Would this argument work? 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 $@ Key Presses in Python I am trying to set multiple definition queries for one layer based on one field using python.  ie.  I have a City layer with a field that holds the city name.  I want a copy of the layer in an MXD with the Definition query set for each value in the City field.  So essentially, I have one source layer, with a copy of the layer as many times as there are values in the City field.  The query would look like this: CITY = 'Atlanta'