I'm getting a lot of errors like this:  W: An error occurred during the signature verification.  The repository is not updated and the previous index files will be used.  GPG error: http://ftp.uk.debian.org/debian stretch-updates  InRelease: The following signatures couldn't be verified because the public key  is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010   Tried to add the keys manually using:  sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8B48AD6246925553   and it says imported/processed but I still get the same errors.
When performing apt-get update, I get the following error:   root@ADS3-Debian6:/home/aluno# apt-get update Atingido http://sft.if.usp.br squeeze Release.gpg Ign http://sft.if.usp.br/debian/ squeeze/contrib Translation-en Ign http://sft.if.usp.br/debian/ squeeze/contrib Translation-pt Ign http://sft.if.usp.br/debian/ squeeze/contrib Translation-pt_BR   (...)  Obter:10 http://security.debian.org squeeze/updates/non-free i386 Packages [14 B] Baixados 612 kB em 4s (125 kB/s)                     Lendo listas de pacotes... Pronto There is no public key available for the following key IDs: 8B48AD6246925553
Write access without read access How to change charset of my website to utf8? Let $A$ be an infinite set. For each $a \in A$, let $x_a$ be a non-negative number. Let the value of the series $\sum_{a \in A} x_a$ be the value of the supremum of its finite partial sums, i.e.:      $$\sum_{a \in A} x_a = \sup_{n \geq 0} \sup_{(a_1, \ldots , a_n) \subset A} \left(x_{a_1} + x_{a_1} + \ldots + x_{a_n}\right)$$   (Supremum is well defined even when its value is infinite)       If $\sum_{a \in A} {x_a}$ is finite, prove that the set $A' = \left\{{a \in A | a &gt; 0}\right\}$   is countable.   My guess is that we have to write $A$ as a union of finitely many sets. Scientific visualization - How to replicate instances around a sphere? I want to replicate a protein structure around an icosahedron. Basically a vesicle of protein structure is what we want:  When I am instancing the protein structure using each vertex of the icosahedron it looks like:  However, the tails are supposed to be directed towards the center. How can I make that work? Prove that: $\sqrt{2\sqrt{3\sqrt{4\cdots\sqrt{n}}}}<3,\,\forall n\in\mathbb N.$ Metrizable topological space $X$ with every admissible metric complete then $X$ is compact How to prove:      If $X$ is a metrizable topological space and every admissible metric on $X$ is complete then $X$ is compact.    I was trying with an idea of contradiction and thereby to construct an incomplete metric on $X$. But not able to construct. How to use early stopping properly for training deep neural network? I have a deep neural network model and I need to train it on my dataset which consists of about 100,000 examples, my validation data contains about 1000 examples. Because it takes time to train each example (around 0.5s for each example) and in order to avoid overfitting, I would like to apply early stopping to prevent unnecessary computation. But I am not sure how to properly train my neural network with early stopping, several things I do not quite understand now:   What would be a good validation frequency? Should I check my model on the validation data at the end of each epoch? (My batch size is 1) Is it the case that the first few epochs might yield worse result before it starts converging to better value? In that case, should we train our network for several epochs before checking for early stopping? How to handle the case when the validation loss might go up and down? In that case, early stopping might prevent my model from learning further, right?   Thank you in advance. What is the difference between Fact and Truth? I'm curious about the difference between Fact and Truth. I was searching on the internet if I could find it. But still I'm confused about the exact meaning. I first read the forum discussion here  where an author has given two examples for each like below     A fact is a reality that cannot be logically disputed or rejected. If   I say "fire is hot," I don't care how great your reasoning skills are,   if you touch fire your skin will burn (and don't give me that "but   people can walk on hot coals!" bull. There's a difference between the   transfer of heat through conduction and training one's body to deal   with the agonizing pain of said conduction). Now when I say this, I am   not speaking a truth, I am speaking a fact. If you say "fire is not   hot," you are not lying, you are incorrect. Facts are concrete   realities that no amount of reasoning will change. When one   acknowledges a fact, they are doing just that. Facts are not   discovered, facts are not created, facts are simply acknowledged.      A truth on the other hand, is almost the opposite. Truths are those   things that are not simply acknowledged, but must be discovered, or   created. If I say "God exists," and I possess strong reasoning for the   affirmative of that statement, then God really does exist, that is a   reality. However, if another individual possesses strong reasoning for   the negative, and because of this reasoning they believe that God does   not exist, then that is also a reality. If we were to debate our   ideologies, and my reasoning appeared stronger than theirs, they may   choose to adopt my belief that God does exist. If they do, then the   existence of God is just as true as the nonexistence of God which they   believed a week ago. Truths, as opposed to fact, are much more fluid   and malleable than their empirical counterparts.   and followed by further discussion.  Then I found this . Article from above link says like below:     Facts are notes and lyrics on sheet music.  Truth is what the singer   gives to the listener when she’s brave enough to open up and sing from   her heart.   But still curious about the difference between both of them.  In our daily life, in general conversation, we generally use these both terms interchangeably. Then what is the difference? Are they synonym or have specific difference? This question follow's JeffE's comment :     In most industries, a PhD has negative value.   I am curious about what potential negatives there may be with having a PhD, particularly in industries.  For example, my PhD has applications for image sensors, and the potential of working in that field is appealing—would having a PhD be a potential barrier? Would it be a case of how explicit the practicalities of the PhD can be made?  Would this make any difference? I want to hatch the area under a curve (graph of a function) with oblique lines on an interval (to illustrate the function's integral on that interval). This can be done elegantly in gnuplot...   ...but I simply cannot reproduce this with pgfplots. The only solution I managed to find with google is the use of the patterns tikz library, however it is unacceptibly ugly:    I'm not aware of any way to alter the color, line width and - especially - the distance between the hatching lines when patterns library is employed. Is there any way to set it? (So that I can change it to resemble the gnuplot version.)  Or, should I choose a completely different approach to reproduce the gnuplot-style hatching...?  Also note that   pgfplots changes the color of the x-axis to red on the interval (which is not a critical problem, of course, but not elegant). the legend for the filling is much more logical in case of gnuplot. Can I reproduce it with pgfplots?   Here is the code I currently use:  \begin{figure}[ht!] \centering \begin{tikzpicture}     \begin{axis}[xmin=-4,xmax=4,xlabel={z},ymin=0,ymax=1]      \addplot[color=red,domain=-4:4,samples=100] {1/sqrt(2*pi)*exp(-x^2/2)};     \addlegendentry{z}     \addplot[color=red,fill=red, pattern=north east lines,  domain=0:1,samples=100] {1/sqrt(2*pi)*exp(-x^2/2)} \closedcycle;     \addlegendentry{Interval}     \end{axis} \end{tikzpicture} \end{figure} The only solution that I have been able to come up with is $d=1$, but because $d&gt;2$, I can't seem to figure out how to find a solution. How to Customize the Email template on chatter posts While any of the other sections under &quot;Edit Profile &amp; Settings&quot; do work normally. How to hide a(n) (NTFS) partition from ubuntu I need to hide an NTFS partition from listing in the nautilus. How can I achieve that?   Is there any tool to do that?   And how can I hide files in ubuntu (except . operator) Cannot downgrade wpa_supplicant to fix Wi-Fi connection to a corporate network (WPA2/PEAP with no CA certificate) in Ubuntu 18.04 I recently upgraded my Ubuntu from 16.04 to 18.04 (clean install, full wipe). Now I can no longer connect to the corporate network at my office (perhaps related to these bugs: , ). What proved to fix this issue in Ubuntu 16.04 is the answer to ; Downgrade wpa_supplicant to 2.1.  However, even with the linode repository, this fix can no longer be applied. There is no version for wpa_supplicant below 2.6 to the best of my knowledge for Ubuntu 18.04.  My question is this: How can I downgrade wpa_supplicant to 2.1 for Ubuntu 18.04?  Configuration needed for corporate the wifi connection:   Security: WPA &amp; WPA2 Enterprise Authentication: Protected EAP (PEAP) Checkbox No CA certificate required. Inner authentication: MSCHAPv2 How do I fix a "Unknown configuration key `foreign-architecture' found in your `dpkg' configuration files." error? Why do I get more satisfaction out of participating in SO than out of my job? Alternatively, are there good ways to get more satisfaction out of my job, possibly by leveraging my participation in SO? Is tipping mandatory at Restaurants and Bars in Germany? Applying for a UK Tourist Visa from outside country of origin The problem is to prove that every Hilbert space has a orthonormal basis. We are given Zorn's Lemma, which is taken as an axiom of set theory:  Lemma If X is a nonempty  with the property that every  of X has an upper bound in X, then X has a maximal element.   Given a orthonormal set $E$ in a Hilbert space $H$, it is apparently possible to show that $H$ has an orthonormal basis containing $E$.   I tried to reason as follows: Suppose $E$ is a finite set of $n$ elements. Then one can number the elements of $E$ to create a totally ordered set of orthonormal elements. Then the span $&lt;E&gt;$ can be identified with $R^n$, where each element $v = v_1 e_1 + v_2 e_2 + ... + v_n e_n$ is identified with the vector $(v_1, v_2, ..., v_n)$. On $R^n$ we have a total order, namely the "lexigraphical order" $(x_1,x_2,...,x_n) \leq (y_1,y_2,...,y_n)$ if $x_1 &lt; y_1$ or if $x_1 = y_1$ and $x_2 &lt; y_2$ or if $x_1 = y_1$, $x_2 = y_2$ and $x_3 &lt; y_3$ and so on. Hence $E$ is a totally ordered subset of $H$ and $H$ is a partially ordered set. However, this set doesn't seem to have an upper bound. The set $E$ does have an upper bound. If we define a total order on $E$ only, then X is a partially ordered set satisfying the criteria so X has a maximal element?   This is as far as I got, and I am not sure the entire argument is correct. I don't see how what kind of maximal element I am seeking, since the orthonormal basis of a Hilbert space can have countably infinity number of elements.