I have a friend who claims that you can leave the Schengen area for 1 night, and re-enter, to reset your 90 days.  For example, an Australian could enter Europe and then go for a couple of nights holiday to Morocco, Andorra, or London (any place outside of Schengen), and then return to Paris and have the passport stamped for another 90 days stay in Europe.  They swear by this and claim they know guys doing it for years.  My understanding, which admittedly is just from reading online and not real-world experience, was that we could only spend 90 days out of any 180 days in the Schengen region.    I've also heard other people say, no, you can't do that and if you are caught overstaying then you can be banned from re-entering schengen region for 5 years.  But, I've heard similar stories from several other people about leaving for 1 night making me think there is something to this story even if it's a loophole or a legal grey area (e.g. maybe the person checking at the border when you re-enter has to actually notice a previous stamp in your passport?)  So what are the real rules and facts about tourists staying in the Schengen region on these visa waiver agreements?
I have searched the web a lot and could not find an answer that fits my situation. Here are two links that are quite contradictory:       My situation:  I've visited Portugal in December 2012 for 29 days on a Schengen visa valid from December 1st, 2012 to February 1st, 2013 for research purposes (I am a Ph.D. student). I want to visit Sweden from February 10th, 2013 to May 10th, 2013 (89 days). I have applied for a Schengen visa again (for research). How will the 90/180 rule work in my situation?
How can I make threading more flexible? I would like to know if there are any other tenses or grammatical structures to use for speaking about the future apart from will (perfect tense included), going to, simple and continuous present.  I mean not the obvious ones. For example, simple present (I could never have imagined it could be used for the future).     My mom arrives tomorrow.   I go to the doctor at 4 o'clock this afternoon. $ \int_1^2\int_1^2 \int_1^2 \int_1^2 \frac{x_1+x_2+x_3-x_4}{x_1+x_2+x_3+x_4}dx_1dx_2dx_3dx_4 $ Let's assume we have a table where it has two columns, one an ID and one an hstore column, which stores key/value pairs.  You could query that column as such:  SELECT name, attributes-&gt;'device' as device FROM products WHERE attributes-&gt;'edition'= 'ebook'   Can you create a view for this table where the keys/values appear as columns in the view instead of all in the hstore column?  Example: I have an hstore key where it might have the key of amenity.  I want to create a view showing the the ID and the amenity values in a new view. Show that every monotonic increasing and bounded sequence is Cauchy. Kind of converse of Kolmogorov maximal inequality Let $S_n=\zeta_1+...+\zeta_n$ where $\zeta_i$ are independent with $E\zeta_i=0, E\zeta_i^2=\sigma_i^2&lt;\infty, |\zeta_i|&lt;K$.  Then, $P(\max_{1 \leq m  \leq n}|S_m| \leq x) \leq (x+K)^2/\operatorname{var}(S_n)$.  How do we show this?  The hint says that I should use the fact that $S_n^2-\sum_{m \leq n}\sigma_m^2$ is a martingale. But I am totally clueless....  Any hint would be appreciated! Thanks and regards. I am looking for QGIS function to extract (or detect) edge from a raster, which was referred in here,  as answer by @MappaGnosis.  The name could have changed since then, or it may have been integrated into other tool... I cannot find it in my QGIS Processing Toolbox (2.14.10 and 2.18.2).  There are similar tools such as GRASS "i.zc Zero-crossing" and SAGA "Gaussian filter", but I am hoping to find this QGIS geoalgorithm. mod_security: another rule with same ID I have installed httpd 2.2.15 on CentOS 6.5 (minimal installation with no cPanel) with modsecurity 2.8. When I am starting httpd I am getting this error:  Starting httpd: Syntax error on line 23  of /etc/httpd/conf.d/modsecurity.conf:  ModSecurity: Found another rule with the same id   The line 23 is:  "id:'200000',phase:1,t:none,t:lowercase,pass,nolog,ctl:requestBodyProcessor=XML" I'm having some issues SSH'ing to a server when logged into a particular VM.  From my local PC, I can log in to the server just fine using the command ssh -i .ssh/[my private key] username@domain.  If I then SSH into another unrelated server which also has the same private key and run the above command it will also log in just fine in to the server.  But, when I SSH into a particular OpenStack VM (again has the same private key) on the unrelated server and then SSH in to the server from there I start getting prompted for a passphrase. But a passphrase hasn't been set for the key so inevitably I get a "Permission denied (publickey)." error.  To double check, I removed the private key from the VM and scp'd the private key from my PC into it again and tried the same command I still get prompted for a passphrase.  In other words:   PC - SSH - Server1 = Works fine  PC - SSH - Server2 - SSH - Server1 =     Works fine  PC - SSH - Server2 - SSH - Virtual Machine - SSH - Server 1 =         Asks for a passphrase   What could be the reason behind this? It's definitely the right private key I'm using and it has the appropriate permissions.  Edit - Output of ssh -v -i .ssh/[my private key] username@domain as requested  OpenSSH_7.4p1, OpenSSL 1.0.2k-fips  26 Jan 2017 debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 58: Applying options for * debug1: Connecting to xxx.xxx.xxx.xxx [xxx.xxx.xxx.xxx] port 22. debug1: Connection established. debug1: key_load_public: No such file or directory debug1: identity file /.ssh/[my private key].ppk type -1 debug1: key_load_public: No such file or directory debug1: identity file /.ssh/[my private key].ppk-cert type -1 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_7.4 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.4 debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.4 pat OpenSSH* compat 0x04000000 debug1: Authenticating to xxx.xxx.xxx.xxx:22 as '[my username]' debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: algorithm: curve25519-sha256@libssh.org debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server-&gt;client cipher: chacha20-poly1305@openssh.com MAC: &lt;implicit&gt; compression: none debug1: kex: client-&gt;server cipher: chacha20-poly1305@openssh.com MAC: &lt;implicit&gt; compression: none debug1: kex: curve25519-sha256@libssh.org need=64 dh_need=64 debug1: kex: curve25519-sha256@libssh.org need=64 dh_need=64 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: ecdsa-sha2-nistp256 SHA256:ZiugTjR5fM0E3evOwHoePFKspDQChA0Ab6L0q88KP/g debug1: Host 'xxx.xxx.xxx.xxx' is known and matches the ECDSA host key. debug1: Found key in /home/centos/.ssh/known_hosts:2 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: SSH2_MSG_NEWKEYS received debug1: rekey after 134217728 blocks debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=&lt;rsa-sha2-256,rsa-sha2-512&gt; debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey debug1: Next authentication method: publickey debug1: Trying private key: /.ssh/[my private key].ppk Enter passphrase for key '/.ssh/[my private key].ppk': Enter passphrase for key '/.ssh/[my private key].ppk': Enter passphrase for key '/.ssh/[my private key].ppk': debug1: No more authentication methods to try. Permission denied (publickey). Number of normals from a point to an ellipse From a typical point $P$ inside an ellipse, how many points $Q_i$ on the ellipse have $PQ_i$ normal to the ellipse?  Someone asked me at school many years ago but I don't think I worked it out. How to make X.org listen to remote connections on port 6000? This is on Ubuntu 10.10 (Maverick Meerkat) 64-bit desktop.  I want to make my X server listen to remote connections from clients in other machines on the local network. I know about ssh -X and that is not what I want. I vaguely remember changing something like TCPListen from no to yes, but I don't remember where this change should be applied.  I'm interested in either a GUI method or a CLI one.  PS editing /etc/X11/xinit/xserverrc to remove the -nolisten tcp option and rebooting does not work. What is the fastest algorithm for finding the natural logarithm of a big number? How to use the Bevel node in 2.79b I'd like to know how exactly to use the new bevel node in Blender 2.79b. It's in the manual now, but I've not yet been able to even locate it. How exactly do you use it? What changes when an Alienist becomes an outsider? What I am working with: I am running my self-made Arduino board (in the sense that I use the Arduino bootloader and code editor) at 3.3V, and powered from a Lithium ion battery, which is USB-charged by a corresponding Microchip charger IC.  What I am trying to achieve: I want to measure battery capacity once every minute or so. I have an LCD attached, so the idea is that the overall setup lets me know how the battery is doing at a given moment. The datasheet of the battery has a voltage versus discharge-level curve, and so by measuring the voltage of the battery, I can estimate the remaining capacity (very roughly but enough for me!).  What I did:   (EDIT: Resistor values updated and P-MOSFET switch added based on @stevenvh and @Jonny's suggestions).  I connected a voltage divider from the battery V_plus, with the larger "portion" going to an analog-read-pin (i.e., ADC) on the Arduino/Atmega chip. The divider is 33 KOhm-to-10 KOhm, thus allowing measurement up to 4.1 Volts maximum of the Li-ion battery from my 3.3V level microcontroller. Also, using one of the I/O pins connected to an n-channel MOSFET, I can switch the current through the divider only when I need the measurement. Here is a rough schematic (updated for a 2nd time based on suggestions of @stevenvh and @Nick):     My question:   How is my current setup? My only constraints are: (1) I would like to make a rough measurement of the battery capacity based on the voltage reading, as described above. (2) I would like to prevent the voltage divider from interfering with my charging IC's reading of battery presence (in my original setup, the divider sometimes caused the IC to misread presence even when the battery was absent). Novel from 50s or 60s - Good vs. Evil I'm not sure I recall enough of this story for a good identification, and the below is definitely out of story order, but...  The POV character goes to his home town and finds it different. He later finds that he's trapped in the town; there are two young people who turn out later on to be ... avatars ... of Ormazd and Ahriman, and the town is a battleground; what he is seeing of the town is Ahriman's effect on the town, and he turns out to have some limited ability to see the original town, which is more-or-less Ormazd's version of reality. In the end, Ahriman's avatar is destroyed, and the town restored.  I read this in the '80s or earlier; it was part of my father's collection, and the book was showing its age; I think it more likely to be the '60s rather than the '50s, and was probably by a prominent name in SF, but not one of the Masters. Boundary conditions for calculus of variations in phase space and under canonical transformations This might be a stupid question, but I just don't get it. In Hamiltonian mechanics when examining conditions for a $(\boldsymbol{q},\boldsymbol{p})\rightarrow(\boldsymbol{Q},\boldsymbol{P})$ transformation to be canonical one starts with $$ \dot{q}_ip^i-H(\boldsymbol{q},\boldsymbol{p},t)= \dot{Q}_iP^i-\bar{H}(\boldsymbol{Q},\boldsymbol{P},t)+\frac{d}{dt}W(\boldsymbol{q},\boldsymbol{Q},t)$$ where $\bar{H}$ is the transformed Hamiltonian, and $W$ is the generating function (now a function of $\boldsymbol{q}$ and $\boldsymbol{Q}$). This term shouldn't break Hamilton's principle, since $$ \delta\int_{t_1}^{t_2} dt\frac{d}{dt}W(\boldsymbol{q},\boldsymbol{Q},t)=\delta W(\boldsymbol{q},\boldsymbol{Q},t)|_{t_2}-\delta W(\boldsymbol{q},\boldsymbol{Q},t)|_{t_1}=0-0=0 .$$ But I don't see why the variation of $W$ should disappear at the endpoints (say at $t_1$). Expanding leads to: $$ \delta W(\boldsymbol{q},\boldsymbol{Q},t)|_{t_1}=\left(\frac{\partial W}{\partial q_i}\right)_{t_1}\underbrace{\delta q_i(t_1)}_{=0}+ \left(\frac{\partial W}{\partial Q_i}\right)_{t_1}\delta Q_i(t_1)=\left(\frac{\partial W}{\partial Q_i}\right)_{t_1}\delta Q_i(t_1).$$ $\boldsymbol{Q}$ is itself a function of $\boldsymbol{q}$ and $\boldsymbol{p}$, so $$ \delta Q_i(t_1)=\left(\frac{\partial Q_i}{\partial q_k}\right)_{t_1}\underbrace{\delta q_k(t_1)}_{=0}+\left(\frac{\partial Q_i}{\partial p_k}\right)_{t_1}\delta p_k(t_1)=\left(\frac{\partial Q_i}{\partial p_k}\right)_{t_1}\delta p_k(t_1). $$ It seems as if we also needed the variation of $\boldsymbol{p}$ to vanish at the endpoints, and I don't get this because (at least in cartesian coordinates) $\boldsymbol{p}=m\dot{\boldsymbol{q}}$ and the velocity can be different along the original and the varied orbitals even at the endpoints (they can point in totally different directions), so in general $\delta \dot{\boldsymbol{q}}(t_1)\neq 0$. What am I doing wrong? Can someone help me with this, please? Use of comma separating two adjectives If I had the phrase       two blond haired, blue eyed people    would the comma be out of place?    should I hyphenate "blond haired" and "blue eyed"? Seems like a stupid question, but I'm after a nice solid answer if possible.  I joined SO a while ago to ask the odd question, but recently I'm starting to use it more often.  I've been reviewing the 40 max items (20 first posts/20 late answers) per day, and editing anything I see wrong with them (lots of +2's)... flagging them... etc.  I've also been  per day.  But other than commenting where I can and answering the odd question, I'm only  (1k at the moment).  I might just be overeager, but I was hoping some high-rep users might be able to write a little something on how they earned their stripes?  I've , and to be honest I was hoping I'd get a hit, because it sounds like a stupid question... anyways, here you go!  Also, I'm not referring to how to gain rep on Meta, since it's a bit of a fluke I've earned the rep I have on here. I'm asking about main SO. I added a user to a group, but group permissions on files still have no effect