I can't vote but can accept on low quality review
If an edit was suggested to an answer to my question and I go to this edit, I see the checkmark
What is a "Nested Quantifier" and why is it causing my regex to fail? I have this regex I built and tested in regex buddy.  "_ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}"   When I use this in .Net C#   I receive the exception  "parsing \"_ [ 0-9]{10}+ +[ 0-9]{10}+  +[ 0-9]{6}+  [ 0-9]{2}\" - Nested quantifier +."   What does this error mean? Apparently .net doesn't like the expression.  Here is the regex buddy so u can understand my intention with the regex...  _ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}  Match the characters "_ " literally «_ » Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {1}+»    Exactly 1 times «{1}+» Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}+»    Exactly 2 times «{2}+» Match a single character present in the list below «[ 0-9]{6}+»    Exactly 6 times «{6}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}»    Exactly 2 times «{2}» Match a single character present in the list below «[ 0-9]{2}»    Exactly 2 times «{2}»    The character " " « »    A character in the range between "0" and "9" «0-9»   In short...  What is a Nested quantifier? 1.I will study hard until I get a high score on this exam. 2.I will study hard until I've gotten a high score on this exam.  I think these sentences are grammatically correct. but if I add a specific time, I think these sentences have to be only this one:  3.I will study hard until I get a high score on this exam on July 25th.  And how about these?  a. I'd like to watch all of the holocaust movies present in the world until I've become an expert on it. b. I'd like to watch all of the holocaust movies present in the world until I become an expert on it.  Since there's no a word representing a specific time, both of them are okay, right? And what I'd like to know is the difference between &quot;have gotten&quot; and &quot;get&quot;. What I know about them is we can use &quot;future perfect&quot; to refer to unspecific future event that might happen before some accident. but &quot;get&quot; refers to future event that could be either a specific scheduled event or unspecific future event. that's why if I add a specific time mentioning, I have to use &quot;get&quot;. Better favourites organisation I don't know about anyone else, but I have a reasonable list of favourites now, and it can be rather difficult to find the relevant ones at any given time. Sometimes, I have a specific one in mind, others I just want to see all favourites relating to a specific topic. It would be nice if there were a way to organise my favourites by tag, or OP, or possibly just search them.  How can we improve the favourites feature?  Please post your ideas on how we might improve the favourites feature of the Stack&nbsp;Exchange sites. Try to keep each answer to one idea so that the votes reflect the popularity of a single idea. Based on the question , I got curious. Is there a guide or resource that describes how the price of a ticket is determined?  When you search you often see curious effects like cheaper tickets for a flight from A to B with a layover compared to a direct flight. This seems counter-intuitive from an outsider's perspective since you fly twice. Also one way tickets more expensive than 2 ways.  It can be a short set of rules. Something that helps someone to get started with finding good prices. I know these can be very complex and they probably change over time and over airline interests but there is probably a simplified set of rules that can be enunciated. Let $f \in C [a,b]$ such that $\forall x\exists y$ such that $|f(y)| \leq \frac{1}{2}|f(x)|$. Prove that $\exists c\in [a,b]$ such that $f(c) = 0$. Is Ubuntu compatible with my hardware? Show that one-sided limits always exist for a monotone function (on an interval) Show that one-sided limits always exist for a monotone function on an interval $[a,b]$.  Me attempt:  1) If a function is monotone on an interval $[a,b]$, then $f(a)\le f(x) \le f(b)$ for $x\in[a,b]$. Therefore if there exists left-hand (right-hand) limit of this function at a given point, then it must be finite. Now we must show that a both left-hand and right=hand limits exist. We use the fact that if we take a sequence $(x_n)\rightarrow c^{+} \in [a,b]$ then $f(x_n)$ is bounded and monotone and therefore it is convergent. How can we do pagination in datagridview in winform Problems when adding a fillable PDF form if the page is rotated What's the difference between $\mathbb{R}^2$ and the complex plane? I haven't taken any complex analysis course yet, but now I have this question that relates to it.  Let's have a look at a very simple example. Suppose $x,y$ and $z$ are the Cartesian coordinates and we have a function $z=f(x,y)=\cos(x)+\sin(y)$. However, now I change the $\mathbb{R}^2$ plane $x,y$ to complex plane and make a new function, $z=\cos(t)+i\sin(t)$.  So, can anyone tell me some famous and fundamental differences between complex plane and $\mathbb{R}^2$ by this example, like some features $\mathbb{R}^2 $ has but complex plane doesn't or the other way around. (Actually I am trying to understand why electrical engineers always want to put signal into the complex numbers rather than $\mathbb{R}^2$, if a signal is affected by 2 components)   Thanks for help me out! In order to animate a character so that it grabs an object an throws it, I added a Child-Of constrained and keyframed its influence. In the F-curve Editor I can't set the curve which controls the influence to interpolation-mode Constant without changing the other curves (Which should be linear or bezier).   How can the interpolation mode of a curve changed independently? How can I find just the *.mp3 files with a recursive command like ls -R *.mp3 in a directory that contains several sub-directories and at the end copy these files in a directory that I choose.  Thanks for your support. How can I see all versions of a package that are available in the archive? Is there a way I can see all the versions that are in the archives that I have configured in sources.list. I can see the last version of each archive withapt-get policy, but how can I see them all?  Is there any way that this can also include PPA and anything in sources.list.d? How to parse hex values into a uint? On the uniqueness of the Riemann-Christoffel tensor According to Section 6.2, Gravitation and Cosmology by Weinberg, the Riemann-Christoffel tensor is the only tensor that can be constructed out of the second (or lower) order derivatives of the metric tensor and is linear in the second order derivatives. The reasoning behind the same goes like this:   In a class of frames where $\Gamma^{\lambda}_{\mu\nu} =0$, the transformation rule for $\dfrac{\partial \Gamma^{\lambda}_{\mu\nu}}{\partial x^{\kappa}}$ involves an inhomogeneous term which is symmetric in $\mu$, $\nu$, and $\kappa$. Thus, if one is to construct a tensor which is a linear combination of the first order derivatives of the Christoffel symbol then the only way to do so is by eliminating the inhomogeneous part of the transformation and this could be done only by making the combination explicitly antisymmetric in $\mu$ and $\kappa$. Since in these frames, $R^{\lambda}_{\mu\nu\rho}$ $ = \dfrac{\partial \Gamma^{\lambda}_{\mu\nu}}{\partial x^{\rho}} -  \dfrac{\partial \Gamma^{\lambda}_{\mu\rho}}{\partial x^{\kappa}} $, $R^{\lambda}_{\mu\nu\rho}$ is the only tensor that can be formulated using the second (or lower) order derivatives of the metric tensor and is linear in the second order derivatives.  I think the presented argument can only suffice to prove that $R^{\lambda}_{\mu\nu\rho}$ is the only tensor that can be formulated from the first derivatives of the Christoffel symbol and is linear in them. I can't figure out why this suffices to assert that $R^{\lambda}_{\mu\nu\rho}$  is the only tensor that can be constructed out of the second (or lower) order derivatives of the metric tensor and is linear in the second order derivatives.  Edit: As the metric is covariantly constant, $\dfrac{\partial g_{{\mu}{\nu}}}{\partial x^{\rho}} = \Gamma^{\kappa}_{{\mu}{\rho}}g_{{\kappa}{\nu}}+\Gamma^{\kappa}_{{\nu}{\rho}}g_{{\kappa}{\mu}}$.  Therefore,   $\dfrac{\partial^2 g_{{\mu}{\nu}}}{\partial x^{\xi}\partial x^{\rho}} = \bigg(\dfrac{\partial \Gamma^{\sigma}_{{\mu}{\rho}}}{\partial x^{\xi}} + \Gamma^{\sigma_1}_{{\mu}{\rho}}\Gamma^{\sigma}_{{\sigma_1}{\xi}}\bigg)g_{{\sigma}{\nu}}+\bigg(\dfrac{\partial \Gamma^{\sigma}_{{\nu}{\rho}}}{\partial x^{\xi}} + \Gamma^{\sigma_1}_{{\nu}{\rho}}\Gamma^{\sigma}_{{\sigma_1}{\xi}}\bigg)g_{{\sigma}{\mu}} + \bigg(\Gamma^{\sigma}_{{\mu}{\rho}}\Gamma^{\sigma_1}_{{\nu}{\xi}}+\Gamma^{\sigma}_{{\nu}{\rho}}\Gamma^{\sigma_1}_{{\mu}{\xi}}\bigg)g_{{\sigma}{\sigma_1}} $  Now, if I want to show that the Riemann-Christoffel tensor is the only (non-trivial and independent) tensor that can be formulated out of the linear combinations of the second order derivatives of the metric tensor then I can equivalently show that the above expansion can be expressed linearly in terms of the Riemann-Christoffel tensor. But I am stuck over how to do it. Also, I am a little bit unclear as to what a linear combination means in this context. The coefficient of the second order term can be only a scalar constant or can it be the metric or can it be the metric that is getting summed over any of the indices as well? JavaScript editor within Eclipse Use parameter expansion to modify output of another expansion I'm trying to use the Bash parameter expansions to modify the output of a command substitution or another parameter expansion. The following nested expansions work quite well in Zsh; but result in a &quot;bad substitution&quot; error in Bash: ${${PWD##*/}//trunk/latest}  or ${$(basename $PWD)//trunk/latest}  the output should be the last folder of the $PWD, replaced by latest when my current directory is trunk so /home/user/trunk should become latest Is there a Bash equivalent allowing to chain expansions without relying on variables or pipes? Or do Bash expansions only allows the input to be a string or a plain variable? How to duplicate a div in JavaScript Force a rebuild of the start menu program index/database in Windows 10 With Windows 10 Microsoft migrated to a database-ish solution for indexing programs in search and the start menu, rather than just using a /startmenu/ directory. AFAIK the exact implementation is still pretty unclear, but there is something along those lines.  Updating from 8.1 to 10 causes it to migrate everything from /startmenu/ to the new system, which ignoring issues such as a (seemingly arbitrary) cap of 500 applications, works fine.  However this failed for me, and from googling seems to be an issue from upgrading with an older dev build, which then carried on to RTM.  So does anyone know a way to force a rebuild/re-index of the program library? Rebuilding the system wide index through control panel (also in &lt;=8.1) has no effect. Fancy chapter headings