I just installed Linux Mint on my computer and I'm having a problem with the Lyx application which I never had with Windows. I downloaded it via the software manager, so I was hoping that there wouldn't be any complications during the installation, yet I'm unable to view my document in .pdf format or even save it as one. Also, under Documents->Settings->Document Class, all classes are grayed out and marked as unavailable.  I searched around a little, but I could only find solutions concerning the WIndows and Mac environments, and being a Linux noob, I thought I should ask here since I can't find a solution for the life of me. Is there a way I can solve this?
I had this problem a week or two ago and I posted here but nothing from the suggested solutions seemed to work. I have managed to get some more details on it, in case anyone can help me, because this issue is causing me huge productivity problems and I really want it solved.  So I'm using Linux mint distribution, and I've installed Lyx via the software manager. Every time that I open a new document, I get an error claiming that some files are missing, and until they are installed, compiling the files or exporting them as pdfs is not possible. The file in question is called "extarticle.cls". Additionally, under Document->Settings->Document Class, every document class is marked as unavailable.  Here is the thing though.. this file is not missing... I have located it inside a folder associated with Lyx. It's definitely not missing.  I really need help with this one guys... It's been weeks since the problem came up and I really just want to be rid of it.. Why does this thing not work? Any help?
Proof of $n^2 \leq 2^n$. I am trying to prove that $n^2 \leq 2^n$ for all natural $n$ with $n \ne 3$. My steps are:    induction base case: $n=0:$ $0² \leq 2⁰$ which is okay.    inductive step: $n \rightarrow n+1:$ $(n+1)²\leq2^{n+1}$ $$(n+1)^2 = n^2 + 2n + 1 = ...help...\leq 2^{n+1}$$   I know the bernoulli inequality but don't know where to use it, if I even need to. I have problems when it comes to proving things which are based on orders.. Under what conditions is the difference between a rank $1$, postive semidefinite matrix and a hermitian matrix positive semidefinite? Where can I find a large palette / set of contrasting colors for coloring many datasets on a plot? I need large set (20 and more) of contrasted and easily visually-distinguishable colors for coloring different datasets on a scientific plot (the set of colors should not include white or black, and colors should be as bright as possible).   The plot is generated programmatically and intended to be included in a presentation which will be displayed using a projector.   Are there any ready-made sets of colors for such a task (I need colors as a set of RGB values)?   Or maybe there is some algorithm which generates such a set of colors programmatically (I use  for plot generation)?  P.S. The plot itself may look, for example, similar to this one: Find a file when you know its checksum? I received an email saying documents are /were I read in  in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the height it dropped from.  In this way, it was said, gravity is subject to the conservation of energy principle and cannot change the total energy of an object.  Consider now the maneuver known as a  (also gravity assist) used by space probes such as the . A space probe approaches a planet with velocity $v$, slingshots around, and ends up with velocity $v+2U$, where $U$ is the velocity of the planet.  Consider the energy of the probe. Before, it was $E_i=\frac{1}{2} mv^2$ and after it is $E_f=\frac{1}{2} m(v+2U)^2$. It looks like $E_f$ is much bigger than $E_i$ - but where did the additional energy come from?   Is this not a violation of the conservation of energy principle? I'm trying to get images in my document in two different ways:   On top of the entire page, centered On top of a single column   I tried it with both twocols and multicols. I ruled out twocols because it forces a new page every time you turn it on, because I need the abstract to be wide and the rest of the cover page to be two columns.  Here are some examples of both points (screenshot from a downloaded PDF):   I want to achieve both, but somehow I can only solve the first point with:  \end{multicols}  \begin{figure}   \centering     \includegraphics[width=0.5\textwidth]{figure}   \caption{Dataflow pipeline of the edge detector}   \label{fig:workflowedge} \end{figure}  \begin{multicols}{2}   Is it awkward to turn off multicols, then turn it back on again?  For my second point, I've tried everything, but almost always, the image doesn't show up at all! The only way I can get it to show at all is by specifying the H placement specifier, but that places the image inside the text where I defined it, not on top of the column.  This is my best try, but it hides the image and breaks all references to ??:  \begin{figure}[t!]   \centering     \includegraphics[width=0.25\textwidth]{figure}   \caption{Dataflow pipeline of the edge detector}   \label{fig:workflowedge} \end{figure}   and I'm getting the warning:  Package multicol Warning: Floats and marginpars not allowed inside `multicols' environment!.   How can I make a figure a non-float?  I also tried the figure* environment, but that just creates an image centered on top of the page, like my first point. How can I keep a folder synchronized to an external USB hard drive? I have a growing music collection which I manually keep in sync with an external USB drive. Sometimes I edit their ID3 tags, add or delete a file in either the hard drive or the USB drive, and I would like to keep those changes synchronized between both.  Does Ubuntu has something available that would help me with this scenario? Preferably something easy to use with a UI.  Update: To clarify my question, changes may happen on both the local hard drive or the USB drive, so the sync process must be on both directions. Correcting for multiple kruskal wallis tests Relative pronouns "where" and "when": where can they be omitted? Let $f$ be a real-valued function continuous on $[a,b]$ and differentiable on $(a,b)$. Suppose that $\lim_{x\rightarrow a}f'(x)$ exists. Then, prove that $f$ is differentiable at $a$ and $f'(a)=\lim_{x\rightarrow a}f'(x)$.    It seems like an easy example, but a little bit tricky. I'm not sure which theorems should be used in here.    ==============================================================  Using @David Mitra's advice and @Pete L. Clark's notes I tried to solve this proof. I want to know my proof is correct or not.  By MVT, for $h&gt;0$ and $c_h \in (a,a+h)$ $$\frac{f(a+h)-f(a)}{h}=f'(c_h)$$ and $\lim_{h \rightarrow 0^+}c_h=a$.    Then $$\lim_{h \rightarrow 0^+}\frac{f(a+h)-f(a)}{h}=\lim_{h \rightarrow 0^+}f'(c_h)=\lim_{h \rightarrow 0^+}f'(a)$$   But that's enough? I think I should show something more, but don't know what it is. Add new alias to Gmail without SMTP (forwarding-only address) Sequence of triangles with exponentiated sides Let $a,b,c\in\Bbb R^+$. For any given $n\in\Bbb N$ there exists a triangle with sides $a^n,b^n,c^n$. Show that at least two of $a,b,c$ are equal.   I know that you can create inequalities for $a^n,b^n,c^n$, but what's next? Transferring Money from India Prove $(1-a)(1-b)(1-c)(1-d)\geq abcd$ if $a^2+b^2+c^2+d^2=1$ Let $a,b,c,d\geq0$, $a^2+b^2+c^2+d^2=1$ Prove $\displaystyle (1-a)(1-b)(1-c)(1-d)\geq abcd$ I mutiplied both with $\displaystyle (1+a)(1+b)(1+c)(1+d)$ to use $1-a^2=b^2+c^2+d^2$ and try using the cauchy-schwarz and holder but it is doesn't work. 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