Python3: print dictionary key, if substring matches at a certain position in value
Understanding slice notation
For any matrix $A$, $AA^T$ is symmetric, and thereby diagonalizable (Spectral Theorem). This implies that $AA^T$ has n linearly independent eigenvectors and therefore full rank.  Does this imply that for any matrix $A$, $AA^T$ is always invertible ? I know there is something wrong here because from the above chain we can conclude that a symmetric matrix is always invertible, which is definitely not true.  Could someone please point out where I am going wrong? Is there a specific reason for having a very short window for passengers to get to the boarding gate before closing it? I am not a frequent traveler but it's been like this with all the flights I have been on. Here is the most recent example:  Below is my boarding pass    As you can see Gate Closes at 20:20  Here is the departures board at 18:32, clearly it says that they will announce the boarding gate at 20:10  ?!    I was hoping they will do that earlier but at 19:41 it's still the same    In fact they announced it at 20:11 but since I was freaking out and had to leg it to the gate I didn't have the time to take a photo.  You might think 9 minutes is enough, well below are the times required to reach the gates from the closest place to them     And that's for a healthy young person, no way my grandmother could be able to be at the gates within 9 minutes.  Is there a specific reason? it's not like they allocate the gate dynamically! The staff must have known about the gate hours ago as I don't expect the pilot to drive the airplane from the garage to the gate within 9 minutes? Why does as.factor return a character when used inside apply? I looked around but did not find that anyone has asked this before, but what are the fonts that are standard/recommended while writing academic reports/papers? How do volume control headphones work? A recent question over on  got me to wondering how volume control headphones work.  I don't mean volume control which works by , but the kind of volume control that signals to the device to increase or decrease the signal output.  For instance, according to the , the volume controls are only for apple devices:     Universal Compatibility and Microphone Communication   LP comes with 2 cables for universal compatibility with all modern mobile and audio devices. The 3-Button remote microphone cable is designed for the latest Apple devices, including iPhone®,iPad®, iPod®, and Macbook series. The long audio-only cable and 1/4" adapter is universally compatible with all audio devices and professional equipment.   However this sort of device apparently works with some android phones and the question implies that it works with some computer sound cards on Windows machines too, but not being an Apple buyer (and only recently getting my first smartphone) I haven't seen this sort of thing before. I've done a quick google search, but can't find anything on standards for this technology.   How does this work?   Is it something as simple as shorting left/right/mic channels? If so, could using headphones of this type with equipment that doesn't support this technology, damage that equipment? Is it a serial signal, for instance sent over the mic channel? Does it just require a headphone  connector or a headphone  +microphone TRRS connector?   Does this technique have a name?  Incidentally, is someone could answer this, I can probably look up the rest of the information myself. *8') Is it as standard as it appears, or is everyone just following Apple? Is this something that is patented?   If so, who holds the patent and do they charge a license fee for people to use this technology? If not, is there an open standard for it?    There is some excellent information in  to the question  but it doesn't answer the specifics of how this type of volume (etc.) control works, since it now seems to be rather more common and standard. Suggested edit review should show custom rejection reasons Somewhat similar to , but rather more limited: when Rejecting an edit, not only the count of custom rejection reasons but the actual text of the reasons should be shown, IMO. Just now I  on SO that tidied some code in a trivially correct and substantially superior way because it looked perfectly legitimate and I couldn't understand why anyone would bother with a custom rejection reason. As it turned out, it was code in a question, of course.  In this case, the rejection reason correctly identified the problem, and had I seen it, I would have been reminded of that aspect I had neglected to check. How to host my existing website with Google Drive Google has given me 15GB of storage. Can I host my own website having my own domain? Summation equation for $2^{x-1}$ What is inertia of a body? The definition of  is  "Inertia is the resistance offered by the body whenever its state of motion is changed."   What is inertia of a body? Is inertia actually a force exerted by the body?  If so, then why is there no application of inertia in numerical problems involving application of force on a body? What is the actual application of inertia in theory? Is it possible to only allow specific packages updates from a PPA Sum over all non-evil numbers How to add a browser tab icon (favicon) for a website? My Logitech G5 Laser mouse has 9 buttons but it's SetPoint software only allows 5 of them to be used as "mouse buttons" and the remaining 4 can only be assigned special windows functions (Forward, Back, Cruise Up, etc) or Keystroke Assignments.  Many of the games I play will take up to 10 "MOUSE BUTTON" inputs for in-game actions but wont recognize the remaining 4 buttons even when assigned keystroke assignments.  Is there a way to make these last 4 buttons "Generic Buttons" as well as buttons 3,4,and 5? (1 is left click and 2 is right click).  My other question is if the above is not possible, maybe I can use AutoHotkey to remap keystrokes as assigned by my SetPoint software to mouse button commands?  If so how? How to add texture to fill colors in ggplot2 I have a collection of files and directories with strange names, they contain spaces and the special characters \, *, ), ( and ?. All of them cause problems when I try to use them in the command line or scripts, e.g.:    $ cd space dir bash: cd: space: No such file or directory  $ cat space file cat: space: No such file or directory cat: file: No such file or directory  $ cat ( bash: syntax error near unexpected token `newline'  $ echo content &gt;\ &gt; ^C  $ ls ? (  )  *  ?  \   How do I enter file or directory names that contain special characters in the terminal? I recently tried to change a bulb using an adaptor (converting from a E27 to B22 fitting). After switching on the light fitting the fuse had blown. After inspection it turns out the adapter is faulty and must have caused a short-circuit.  After removing the bulb and resetting the switch in the main fuse box, I am now unable to operate the switch on the wall to turn the fitting off (the switch physically won't click).   Is there something I can do to fix the problem?  Thanks, What is a comprehensive definition of Philosophy? Alternatively, is it impossible to define Philosophy? This is a pseudo- question, but it seems like it belongs here. I am calculating the class group of $\mathbb Q(\sqrt 6)$. My working is as follows:  The Minkowski bound is $\lambda(6)=\sqrt 6&lt;3$ so we only need to look at prime ideals of norm $2$. $2$ divides the discriminant, $24$, of $\mathbb Q(\sqrt 6)$, so $2$ ramifies, and so for any prime ideal $\mathfrak p$ of norm $2$, $\mathfrak p^2$ is principal. But $(2, \sqrt 6)^2=(2)$, so $\mathfrak p=(2, \sqrt 6)$ has norm $2$. If I can show $\mathfrak p$ is not principal, then I can conclude that $Cl(\mathbb Q(\sqrt 6))\cong C_2.$ But if there was an element of $\mathcal O_{\mathbb Q(\sqrt 6)}$ of norm 2, this would correspond to a solution of the diophantine equation $x^2-6y^2=2$. Clearly $x$ is even, so writing $x=2n$ we get $2n^2-3y^2=1$. Now reducing modulo $3$, we get $2n^2\equiv 1 \pmod 3$ which has no soultions. Hence $\mathfrak p$ is not principal and $Cl (\mathbb Q(\sqrt 6)) \cong C_2.$  However,  says that the class group is trivial. Where have I gone wrong? What am I misunderstanding? Is $(2, \sqrt 6)$ principal? List all my drafts In GMAIL you can list all your boss-tell-off and wife-cuss-out emails by clicking Drafts    I'd like to see my started-but-never-finished responses, possibly between x Answers and y Votes in /&lt;&lt;user&gt;&gt;/Stats/? How do I install VMware player on a Mac os X?