I just downloaded the newest iOS version, which I don't know what it is, and I can't download free apps now. I used to be able to download free apps, but now apple requires a credit card to download apps even if the apps are free.  I don't know what version of iOS I am using, nor what type I was using earlier. Nor do I know what type of iPhone I am using other than that it is an iPhone of some sort. I don't know how to find out this information either.
I  want to download free app in my iPod touch device and i have the following doubts.  Kindly resolve me doubts.   when i try to download it asks my credit card security number. since i am trying to download free app , why do i need to provide my credit card security code? Will i be debited for downloading the free app from app store?   I cant able to find any information regarding this on apple.  Please provide me some references about this from apple and please resolve my doubts.  Thanks a lot.
How do I copy files using Windows Batch? How to define a bijection between $(0,1)$ and $(0,1]$? I am a student who has taken the basic calculus courses but I am working through Calculus (the fourth edition) by Spivak in my spare time in order to both review the material and to gain a more rigorous understanding of the concepts. I am currently in Chapter 8 where he supplies a proof of the basis of the Intermediate Value Theorem, Theorem 7-1 (pp. 135-136 of the fourth edition). It seems mostly straightforward but I think there is some nuance of it that I don't grasp.  I am including in this post the statement Theorem 6-3 since he references it in the proof of Theorem 7-1 as well as part of Theorem 7-1 itself.     Theorem 6-3 Suppose $f$ is continuous at $a$, and $f(a) &gt; 0$. Then $f(x) &gt; 0$ for all $x$ in some interval containing $a$; more precisely, there is a number $\delta &gt; 0$ such that $f(x) &gt; 0$ for all $x$ satisfying $|x-a| &lt; \delta$. Similarly, if $f(a) &lt; 0$, then there is a number $\delta &gt; 0$ such that $f(x) &lt; 0$ for all $x$ satisfying $|x-a| &lt; \delta$.     Problem 6-16 is also referenced. However,it is the same thing as Theorem 6-3 for one-sided limits. The following proof is the Theorem 7-1 up through the paragraph which I don't fully understand.     Theorem 7-1: If $f$ is continuous on $[a,b]$ and $f(a) &lt; 0 &lt; f(b)$, then there is some number $z$ in $[a,b]$ such that $f(x) = 0$.  Proof: Define the set $A$ as follows:  $$A = \{x : a \le x\le b, \mbox{ and } f \mbox{ is negative on the interval } [a,x] \}.$$  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Clearly $A \ne \emptyset$, since $a$ is in $A$; in fact, there is some $\delta &gt; 0$ such that $A$ contains all points $x$ satisfying $a \le x &lt; a + \delta$; this follows from Problem 6-16, since $f$ is continuous on $[a,b]$ and $f(a)&lt;0$. Similarly, $b$ is an upper bound for $A$ and, in fact, there is a $\delta &gt; 0$ such that all points $x$ satisfying $b-\delta &lt; x \le b$ are upper bounds for $A$; this also follows from Problem 6-16, since $f(b) &gt; 0$. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; From these remarks it follows that $A$ has a least upper bound $\alpha$ and that $a &lt; \alpha &lt; b$. We now wish to show that $f(\alpha) = 0$, by eliminating the possibilities $f(\alpha) &lt; 0$ and $f(\alpha) &gt; 0$. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Suppose first that $f(\alpha) &lt; 0$. By Theorem 6-3, there is a $\delta &gt; 0$ such that $f(x) &lt; 0$ for $\alpha - \delta &lt; x &lt; \alpha + \delta$. Now there is some number $x_0$ in $A$ which satisfies $\alpha - \delta &lt; x_0 &lt; \alpha$ (because otherwise $\alpha$ would not be the least upper bound of $A$). This means that $f$ is negative on the whole interval $[a,x_0]$. But if $x_1$ is a number between $\alpha$ and $\alpha+\delta$, then $f$ is also negative on the whole interval $[x_0,x_1]$. Therefore $f$ is negative on the interval $[a,x_1]$, so $x_1$ is in $A$. But this contradicts the fact that $\alpha$ is an upper bound for $A$; our original assumption that $f(\alpha) &lt; 0$ must be false.    The point I don't understand is in the final paragraph of the excerpt. Why does Spivak split the interval $[a,b]$ up into the subintervals $\lbrack a,x_0 \rbrack$ and $[x_0,x_1]$? Isn't it true that, because $\alpha$ is a least upper bound of $A$ and $f$ is continuous on $[a,b]$, it must be true that if $a \le x &lt; \alpha$ then $f(x)&lt;0$? I understand the need to pick out the $x_1$ but not the $x_0$. Especially perplexing is the statement "there is some number $x_0$ in $A$ which satisfies $\alpha - \delta &lt; x_0 &lt; \alpha$ (because otherwise $\alpha$ would not be the least upper bound of $A$." Wouldn't it be true that if there were some $x_0$ such that $a \le x_0 &lt; \alpha$ and $f(x_0) \ge 0$ that $x_0$ would be an upper bound for $A$, contradicting that $\alpha$ is the least upper bound of $A$?  Thanks for any help. Transformation issue with SVG to GeoJSON conversion I have a vector image in SVG format. (without georeferences)    I am trying to display it using OpenLayers to display properties of different polygons in it.  I tried converting it to GeoJSON but the resulting render appears to be stretched (ratios are not preserved).  Is there a transformation or a map projection that I am missing or recreating a GeoJSON from scratch the only relevant choice? How to filter by messages, not by conversation? I have been emailing my Gmail account error messages from a project I am working on.   I am trying to use Gmail filters/labels to sort out the class of errors.  But because the subject line is basically always the same even if I have a specific filter for 3 known error cases, the label is applied to the conversation, instead of the specific message.  Therefore, all the errors get all the filters.  I do not yet want to delete the errors, but would rather file them separately.   I have not yet used the NOT contains string yet, but that looks to be non-scalable as I get to the fourth or fifth error case I am done with handling.  Is there any option other than turning off Conversations for all my email?  (I guess I could use one of my spare accounts to turn off conversations and do the work there but would be nice to have such an option). I'm trying to remember a cartoon tv show where the main boy, a blonde girl, and another boy capture monsters. There was something about a 'veil' between their world and the monster world, but a 'secret society' of sorts stopped the monsters from crossing, or used them to battle the people who wanted to use them for evil led by a wise old lady. I'm pretty sure they trapped monsters into pieces of jewelry or clothing.   Not so sure about this part: and they had these 'supernatural powers' that were connected to their 'aura' and they could travel from place to place with it.   (Another brown haired girl joined because she found out? There was an arc where the blonde got jealous and the monster she controlled attacked the brown haired girl?)  I can't remember much of it, but I remember in the end the 'veil' was broken and monsters flew over the city. And the main boy and the blonde girl held hands... or kissed? If I'm floating in space and I turn on a flashlight, will I accelerate? Photons have no mass but they can push things, as evidenced by .   Can photons push the source which is emitting them? If yes, will a more intense flashlight accelerate me more? Does the wavelength of the light matter? Is this practical for space propulsion? Doesn't it defy the law of momentum conservation?  Note: As John Rennie mentioned, all in all the wavelength doesn't matter, but for a more accurate answer regarding that, see the comments in  .  Related Wikipedia articles: , Need to prove that $(S,\cdot)$ defined by the binary operation $a\cdot b = a+b+ab$ is an abelian group on $S = \Bbb R \setminus \{-1\}$. So basically this proof centers around proving that (S,*) is a group, as it's quite easy to see that it's abelian as both addition and multiplication are commutative. My issue is finding an identity element, other than 0. Because if 0 is the identity element, then this group won't have inverses.  The set explicitly excludes -1, which I found to be its identity element, which makes going about proving that this is a group mighty difficult. Is there a word which describes terms that are spelled like a particular pronunciation? Some examples: &quot;never&quot; might be written as &quot;neva&quot; &quot;I don't know&quot; is sometimes written as &quot;iono&quot; or &quot;I dunno&quot; on various internet media. My question is: is there a word for this particular technique of spelling a term in the way it is (sometimes) pronounced? I know this is a really basic question, but I've just started with some basic C++ programming after coding a few projects with high-level languages.   Basically I have three questions:   Why use pointers over normal variables? When and where should I use pointers? How do you use pointers with arrays? As well as many of the other features talked about during macOS Mojave's release like dark mode and the addition of new apps like Home, another key feature of macOS Mojave seems to be it's heightened focus on both privacy and security.   As quoted under the "Camera and Microphone Now Require Your Permission" section of  article:      Apple also announced that other categories of data, such as your Messages history and Mail database, will be protected in a similar manner to macOS Mojave's new camera and microphone permissions.   I understand that after the update, when an app requests to use your camera or microphone, you will receive an alert like the one below:    However, I am more intrigued by the following:     ...other categories of data, such as your Messages history and Mail database, will be protected in a similar manner...   I have been unable to find much information about this online and I do not currently have the pre-release version of macOS Mojave installed and am therefore unable to test this new feature but I am curious to know what exactly this feature will mean.   Has Apple publicly documented how this will work? I can't seem to get Python to import a module in a subfolder. I get the error when I try to create an instance of the class from the imported module, but the import itself succeeds. Here is my directory structure:  Server     -server.py     -Models         --user.py   Here's the contents of server.py:  from sys import path from os import getcwd path.append(getcwd() + "\\models") #Yes, i'm on windows print path import user  u=user.User() #error on this line   And user.py:  class User(Entity):     using_options(tablename='users')      username = Field(String(15))     password = Field(String(64))     email    = Field(String(50))     status   = Field(Integer)     created  = Field(DateTime)   The error is: AttributeError: 'module' object has no attribute 'User' How can I combine multiple rows into a comma-delimited list in Oracle? I have a simple query:  select * from countries   with the following results:  country_name ------------ Albania Andorra Antigua .....   I would like to return the results in one row, so like this:  Albania, Andorra, Antigua, ...   Of course, I can write a PL/SQL function to do the job (I already did in Oracle 10g), but is there a nicer, preferably non-Oracle-specific solution (or may be a built-in function) for this task?  I would generally use it to avoid multiple rows in a sub-query, so if a person has more then one citizenship, I do not want her/him to be a duplicate in the list.  My question is based on the similar question on .  UPDATE: My function looks like this:  CREATE OR REPLACE FUNCTION APPEND_FIELD (sqlstr in varchar2, sep in varchar2 ) return varchar2 is ret varchar2(4000) := ''; TYPE cur_typ IS REF CURSOR; rec cur_typ; field varchar2(4000); begin      OPEN rec FOR sqlstr;      LOOP          FETCH rec INTO field;          EXIT WHEN rec%NOTFOUND;          ret := ret || field || sep;      END LOOP;      if length(ret) = 0 then           RETURN '';      else           RETURN substr(ret,1,length(ret)-length(sep));      end if; end; Electromagnetic waves in vacuum If there is no source then also there is electromagnetic waves described by Maxwell equation. how if there is no source then existence of EM waves. What gives energy to this EM  waves. Is it vacuum fluctuation or something else? How to turn cheats on or off Invariance of a maximally entangled state under unitary operation $U \otimes U^\dagger$ Apparently the (d-dimensional) maximally entangled state, $|E \rangle = \sum_{i} |ii\rangle /\sqrt{d}$ is invariant under operations of the form $U \otimes U^\dagger$. I want to prove this result, which amounts to showing that  $$\left(\sum_i U | i \rangle \otimes V |i \rangle = \sum_i | ii \rangle \right)\Rightarrow (V = U^\dagger )$$  I have no idea how to even start. I suppose it's some simple linear algebra result, but I don't see it. A hint would be appreciated. How to saveHTML of DOMDocument without HTML wrapper? Number of bitstrings with $000$ as substring I have $F_n$ number of bitstrings that have $000$, How would I prove that for $n \ge 4$ , $a_n = a_{n-1} +a_{n-2}+a_{n-3}+ 2^{n-3}$?  Now there are many  ways to go about this but if I choose starting a $n-3$ bit string and append it with $000$ how would I show that? Can't install Oracle JDK 9 I uninstalled jdk packages and now can't install them back. I managed to install oracle-java7-installer and oracle-java8-installer but can't install oracle-java9-installer. It seems that my computer tries to download wrong version of oracle-java9-installer 177 when version i would be able to download is 178.    $ wget http://download.java.net/java/jdk9/archive/178/binaries/jdk-9+178_linux-x64_bin.tar.gz --2017-07-21 11:00:02--  http://download.java.net/java/jdk9/archive/178/binaries/jdk-9+178_linux-x64_bin.tar.gz Connecting to 10.144.1.10:8080... connected. Proxy request sent, awaiting response... 200 OK Length: 293348142 (280M) [application/x-gzip] Saving to: 'jdk-9+178_linux-x64_bin.tar.gz'  jdk-9+178_linux-x64_bin.tar.gz     1%[&gt;                                                          ]   5.42M  5.04MB/s               ^C  $ wget http://download.java.net/java/jdk9/archive/177/binaries/jdk-9+177_linux-x64_bin.tar.gz --2017-07-21 11:00:16--  http://download.java.net/java/jdk9/archive/177/binaries/jdk-9+177_linux-x64_bin.tar.gz Connecting to 10.144.1.10:8080... connected. Proxy request sent, awaiting response... 404 Not Found 2017-07-21 11:00:17 ERROR 404: Not Found.   Can you help? apt-get tries to install Oracle JDK 9.  I run Ubuntu 16.04 in virtual machine hosted by win7  Full error message:  sudo apt-get install oracle-java9-installer Reading package lists... Done Building dependency tree        Reading state information... Done oracle-java9-installer is already the newest version (9b177-1~webupd8~0). 0 upgraded, 0 newly installed, 0 to remove and 147 not upgraded. 1 not fully installed or removed. After this operation, 0 B of additional disk space will be used. Do you want to continue? [Y/n] Y Setting up oracle-java9-installer (9b177-1~webupd8~0) ... Using wget settings from /var/cache/oracle-jdk9-installer/wgetrc Downloading Oracle Java 9... --2017-07-21 10:54:11--  http://download.java.net/java/jdk9/archive/177/binaries/jdk-9+177_linux-x64_bin.tar.gz Connecting to 10.144.1.10:8080... connected. Proxy request sent, awaiting response... 404 Not Found 2017-07-21 10:54:13 ERROR 404: Not Found.  download failed Oracle JDK 9 is NOT installed. dpkg: error processing package oracle-java9-installer (--configure):  subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing:  oracle-java9-installerE: Sub-process /usr/bin/dpkg returned an error code (1) What exactly do quotation marks around the table name do? I thought that the quotation mark (") was simply a type of grouping marker but I'm debugging some NHibernate code and notice that while  SELECT * FROM site WHERE site_id = 3;   Works fine  SELECT * FROM "site" WHERE site_id = 3;   fails with a table or view does not exist error.  What gives?