How can I add and remove items from my set concurrently?
concurrentModificationException
Is there to make the login screen appear on the external display in 18.04? On Ubuntu 18.04, I have connected my laptop to an external display and I am able to set the external display as primary and external display only mode. But when I turn on my laptop or log out from my session the display login screen is displayed only on my(internal) laptop screen. But once I login the display switches to external only and my laptop screen turns off as expected. Is there a way I can make the login screen appear only on the external screen on bootup or on logout as in 16.04? Also the login screen does not follow my cursor as in 16.04. \nameref breaks for the star versions of section, paragraph when titlesec is loaded. I have a document that numbers paragraphs by default, but I have a few I do not want to number but would like to refer to. These are marked with \paragraph*, however, if the titlesec package is loaded at the same time, it causes nameref to display an empty string (the link box of hyperref is still visible).  MWE:  \documentclass[12pt]{article} \usepackage[sf]{titlesec} %comment this out and it works fine. \usepackage{hyperref} \begin{document} \section{Sections} \label{sec} This is \nameref{sec} \paragraph{A named Paragraph} \label{par} This is \nameref{par} \paragraph*{A starred named Paragraph} \label{par:star} This is \nameref{par:star} \end{document}   I suspect titlesec causes this defect for ALL star variants of sectioning commands but have not tested this. For me only paragraph* is relevant however a fix for all variants would be the best.  I have a hunch it might be related to this:  however this happens to go way beyond my latex knowledge and is just "magic" for me. Color Transfer from colored image into grayscale image The Degree of Zero Polynomial. I wonder why the degree of the zero polynomial is $-\infty$ ?  I heard that, it is $-\infty$ to make the formula $\deg(fg)=\deg(f)+\deg(g)$ hold when one of these polynomials is zero. However, if that was the only reason we could have said that it is $\infty$ instead. If the laws of random variables weakly converge to a point mass at $c$, then the random variables converge in probability to $c$. This is question 10.3.1 from Rosenthal's First Look at Rigorous Probability.  Suppose $\mathcal{L}(X_n) \Rightarrow \delta_c$ for some $c \in \mathbb{R}$. Prove that $\{X_n\}$ converges to $c$ in probability.  Here $\mathcal{L}(X_n)$ refers to the distribution of $X_n$.  Is the following proof correct?  Is a simpler proof available?  Is there a simple proof using Skorohod's theorem?  I attempted to prove the contrapositive. Suppose $X_n \not \to c$ in probability.  This means that there is an $\varepsilon &gt; 0$ so that for all $N$, there exists an $m &gt; N$ such that  \begin{equation}   P(|X_m - c| \geq \varepsilon) &gt; \eta, \text{ for some $\eta &gt; 0$}. \end{equation}  Consider  \begin{equation}   B := \{x \in \mathbb{R} : |x - c| \leq \varepsilon\} \in \mathcal{B} \text{ the Borel sets on $\mathbb{R}$}. \end{equation}  Then $B^c \in \mathcal{B}$ and denoting the distribution of $X_n$ as $\mu_n$ we have  \begin{equation}   \mu_n(B^c) = P(X_n \in B^c) = P(|X_n - c| \geq \varepsilon) &gt; \eta. \end{equation}  For all $N$, there exists an $m &gt; N$ such that the cumulative distribution function of $X_m$ is not the same as the cumulative distribution function of $\delta_c$; in particular it's mass changes somewhere at least $\varepsilon$ distance from $c$. Finally because $\delta_c(\{x\}) = 0$ for all $x \neq c$ this completes the proof. Pattern Match symbols that begin with same letter? I'm a physics teacher and I would like to find a simulation software that could be used to give exact numerical answers to high school level problems in Newtonian mechanics.  I want the students to first calcultate a numerical answer to a physics problem and then use the simulator to visualize the problem in order to understand it better and verify that the simlator gives the same answer that they got when doing the calculation themselves.  Here are some examples of what kind of problems I want the students to be able to solve with the simulator:   A slope with a specific angle of inclination and a ball starts rolling at a certain point. Determine the speed, angular momentum and total mechanical energy of the ball after a specific time t. A ladder of known mass and length is leaning against the wall at a specific angle. The contact between the ladder and the wall is frictionless. Calcultate the x and y components of the force between the floor and the ladder.   I would like the software to have the following features:  - Simulation in 2D. No 3D simulations are necessary and the software should at least have the option of doing simulations only in 2D.  - Position all objects exactly by writing numbers (just positioning the objects using the mouse is not precise enough).  - Show animations of the time evolution of the system.  - Show forces, velocities and accelerations as arrows.  - Give exact numerical results so that the students can use the software to verify their calculation.  Ideally the software would have a graphical user interface, but if no suitable software with graphical interface exixts, I could also consider a software with text-based inputs. I would consider both free and commercial software.  My question is: Is there any software that would meet these requirements and if there is, where could I get it? Can I mix sources from different ubuntu versions? As we know that we are using  for installing packages and repositories configuration file located at /etc/apt/sources.list.  I am using Ubuntu 12.10 (Quantal Quetzal) which reaches . That means no updates or support. So, the question is, can I use sources.list file from another version, say Ubuntu 12.04 LTS, and will it negatively affect the system. Proof with 3D vectors Let ${a} = \begin{pmatrix}x_a\\y_a\\z_a\end{pmatrix}$, ${b} = \begin{pmatrix}x_b\\y_b\\z_b\end{pmatrix}$, and ${c} = \begin{pmatrix}x_c\\y_c\\z_c\end{pmatrix}$. Show that $(x_a,y_a,z_a)$, $(x_b,y_b,z_b)$, and $(x_c,y_c,z_c)$ are collinear if and only if ${a} \times {b} + {b} \times {c} + {c} \times {a} ={0}.$  Hello,  Is there any other way to do this problem without bashing?  I can't seem to find a nice and slick solution to this.  Thanks in advance! Flattening iterator I want to be able to have LinkedList.contains() return true for a custom comparator.  Suppose that I have 1 LinkedList and 2 objects  LinkedList&lt;MyObject&gt; myList = new LinkedList&lt;MyObject&gt;();  MyObject a = new MyObject("HELLO"); MyObject b = new MyObject("HELLO");   Technicaly, both objects are identical in terms of comparison (MyObject implements Comparable)   ( a == b ) == true  however, when I do the following, myList does not return true for myList.contains(b)  myList.add(a) myList.contains(b) // == false   I think its because contains will check object reference and see that a and b are 2 distinct objects. Is there any way I can make it so I don't have to extend LinkedList to compare those objects? How can I tell how long (more or less) it will take me to complete a game? I'm going down my huge backlog of unplayed Steam games and I'm thinking the best way to tackle the list is to go through the shortest games first and then concentrate on the 20+ hour ones. I'm wondering if there's a website or something else that has an estimated amount of gameplay time for games.   Is there anything like that? How do I add arrowheads to circular arcs? I have seen the word 'only' placed both before and after a noun. Where should the word 'only' go in this sentence? Is it the writer's choice?   If you have attended every lesson, only the songs need to be rehearsed at home. If you have attended every lesson, the songs only need to be rehearsed at home. Is conservation of momentum and energy valid for non-inertial frames? How to get product recommendations This next year, I am helping an effort to clean several SQL Server environments.    We have about 10,000 stored procedures and estimate that only about 1000 of them are used on a regular basis, and another 200 or so are used on a rare occasion, meaning we have a lot of work to do.    Since we have multiple departments and teams that can access these databases and procedures, we are not always the ones calling the procedures, meaning that we must determine what procedures are being called.  On top of that, we want to determine this over a few months, not in a few days (which eliminates some possibilities).  One approach to this is to use the SQL Server Profiler and track what procedures are being called and compare them to the list of what procedures we have, while marking whether the procedures are used or not.  From then, we could move the procedures to a different schema in case a department comes screaming.  Is using the Profiler the most effective approach here?  And/Or have any of you done something similar and found another way/better way to do this? Why is my camera metering indoor scenes as darker than I expect, forcing me to use a high ISO? I am shooting in natural light, with my subject facing a full floor-to-ceiling south facing window. You would think my meter would allow ISO between 200-400 in bright light, but I was lucky to get it to 640, with f/3.2 and 1/60 (manual mode).  I've read other places that people say put your ISO down to 100 for indoor shots for greatest clarity (especially sharp eyes) — but don't know how I can with subjects potentially moving. Is there a setting in my camera (Canon 5D Mark III) I am missing, or something that might be making my meter need more light? Can you Start Skyrim 'silent' without the launcher showing up? I bought a new MacBook Air and was able to connect to the internet at first but now it won't connect.  I have other devices as well as other computers on wifi but my Mac won't connect.  When I try and click on the wifi, it tells me that it can't be joined.  How can I troubleshoot?