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How to make sure I'm not using any proprietary software after installation? I know I can check the currently installed non-free software with the following command (assuming aptitude is FOSS):  aptitude search '?installed (?section(restricted) | ?section(multiverse))'   And I can remove the "restricted" and "multiverse" sources (and not add any PPA's) to keep that list empty. I'm assuming from this point, whenever I apt install something, that something is either in the allowed sources or it is not found.  Is this enough? Does this make sure all software I'm running (in Ubuntu) is open-source? Given that $xyz=1$, prove that $\frac{x}{1+x^4}+\frac{y}{1+y^4}+\frac{z}{1+z^4}\le \frac{3}{2}$ Given that $xyz=1$, prove that $$\frac{x}{1+x^4}+\frac{y}{1+y^4}+\frac{z}{1+z^4}\le\frac{3}{2}.$$  I proved this with , but: is there a better/more elegant way? The forgetful functor $\mathsf{Groups} \to \mathsf{Sets}$ admits a left adjoint, namely, "forming the free group" functor.  I was wondering if this has a left adjoint.  This seems unlikely, but I don't have a proof.  Is there a functor $\mathsf{Sets} \to \mathsf{Groups}$ that admits a left adjoint at all? IF statement inside a LINQ SELECT Why can't the indefinite integral $\int\frac{\sin(x)}{x}\mathrm dx$ be found? Encopresis, I'm at my wits end? Does anybody have suggestions? Bluetooth earphones work fine until sleep. After resuming from sleep however, they appear to connect for a brief moment before disconnecting. On blueman, the error given is Resource temporarily unavailable. This issue arose only after updating to 18.04 LTS.   Here's the terminal output for lsusb:  Bus 001 Device 002: ID 8087:8001 Intel Corp.  Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 002 Device 004: ID 1bcf:0002 Sunplus Innovation Technology Inc.  Bus 002 Device 003: ID 04f2:b477 Chicony Electronics Co., Ltd  Bus 002 Device 002: ID 0a5c:21f1 Broadcom Corp. HP Portable Bumble Bee Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub What is the difference between linear equation and linear regression? I am using linear equation to find the correlation of values of x, y and z  3x + 4y + 2z = 6 4x + 1y + 4z = 17 8x + 2y + 5z = 9   I would like to know the difference between linear equation and linear regression. Is it the same in approach? Is the integral $\int_0^\infty \frac{\mathrm{d} x}{(1+x^2)(1+x^a)}$ equal for all $a \neq 0$? Let $a$ be a non-zero real number. Is it true that the value of $$\int\limits_0^\infty \frac{\mathrm{d} x}{(1+x^2)(1+x^a)}$$  is independent on $a$? My competitor is using Alexa to see what I am doing. I need to get stop Alexa from including my sites in their rankings. How can I do so?   Is it possible to deny access to any visitor with the Alexa toolbar and deny access to Alexa bot requests? Subdivision surface modifier problem Hello!   I've recently started learning Blender and faced one problem.  After applying subdivision surface modifier I have plenty of extra faces. I've watched some teaching videos and I suppose additional faces shouldn't be added. Is it OK ? How to avoid this problem if it isn't. How to show that $K\leq S_4$ is a normal subgroup? Let $K=\{(1),(1,2),(3,4),(2,4),(1,4),(2,3)\}$ is a subgrope of $S_4$, we want to show that it is a normal subgroup.  I know that i have to examine the condition of normality in $S_4$ i.e. for all $g\in S_4, g^{-1}Kg=K$. I think this takes times or I am missing something near. Please give me the right hint. Thank you.  Edit: $K = \{(1),(12)(34),(13)(24),(14)(23)\}.$ Tag scores update is supposed to happen at 03:00 UTC every day. Tag scores are updated by a scheduled job that is time consuming and often times out  (see for example the answers for  and ).  In the past month or two, the issue with not updating the scores has gotten much worse. Tag scores are now regularly not updated for 2-3 days in a row. The job fails more often than it runs which obviously lowers usability and appeal of tag badges (which are not awarded when the script fails) and scores to some extent.  I can also guess that if a job fails on consecutive days, it only makes it harder to make it work as it has more and more tags and answers to recount.  This issue happened in the past but not to the extent it's happening now.  Please do not close it as duplicate. I'm creating a separate post as I've been asked to do it by Adam Lear in a comment for the answer for the first of the linked questions. Other posts reporting this issue have accepted answers which makes them difficult to track for the SE team.  UPDATE  I've been writing down whether the scores were updated or not every day in April.  The results are:  Day      1   2   3   4   5   6   7   8   9   10  11  12  13  14  15   Updated  -   -   -   ✓   -   ✓  -   -   -   -   -   ✓   -   -   -   Day      16  17  18  19  20  21  22  23  24  25  26  27  28  29  30 Updated  ✓   -   ✓   -   ✓   -   -   ✓  ✓   -   ✓  -   ✓   -   -   The update succeeded on 10 days, failed on 20. The situation got somewhat better in the second half of the month. Has something been done about it? Is it possible to get a list of most recently installed packages? $2 \otimes_{R} 2 + x \otimes_{R} x$ is not a simple tensor in $I \otimes_R I$ Gravity in 2d space and inverse linear law In our three-dimensional universe, gravity obeys the inverse square law. In a four-dimensional universe, gravity would be expected to obey the inverse cube law et cetera.  In a two-dimensional universe, one would similarly expect gravity to obey an inverse linear law. I've seen it claimed that this is not actually true, when you work it out according to general relativity there would actually be no gravity at all in such a universe. Is this true? If so, is there a layman's explanation of why? Is it related to the fact that gravitational potential wells would be infinitely deep?  Would electrostatic forces follow the same law as gravity?  If there existed infinitely long strings in our universe, would they have the same gravitational effect as point particles in a 2d universe? How to kill The Twins In Terraria In Terraria I often try to defeat spazmatism first, but when he transformed, his flamethrower killed me. What is easiest way to kill The Twins? Always sort Recent Places by date modifed How to print paragraphs in twig template? I have a content type, basic, where i have added a Paragraph field field_pr that has two fields: field_text, field_color. I have a twig template node--basic--full.html.twig where I want to print the value of the paragraph field node.field_pr.   node.field_pr can have between one and ten paragraph values.   When I print the array for content.field_pr, I get a huge array. However, I only want the values from the field_pr.field_text and field_pr.field_color. How would I be able to do this from the node twig template?   I have tried the following but cannot seem to access the values. What am I missing?  {% for field in content.field_pr %}    {{ field[loop.index0].entity.field_text.value }}    {{ field[loop.index0].entity.field_color.value }} {% endfor %}  {% for field in content.field_pr %}    {{ field[loop.index0]['#paragraph'].field_text.value }}    {{ field[loop.index0]['#paragraph'].field_color.value }} {% endfor %}   Here is an image of the array that is printed for the node.field_pr field. Significance of $\sqrt[n]{a^n} $?! There is a formula given in my module:  $$ \sqrt[n]{a^n} = \begin{cases}  \, a  &amp;\text{ if $n$ is odd } \\  |a| &amp;\text{ if $n$ is even } \end{cases} $$  I don't really understand the differences between them, kindly explain with an example.