<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE chapter SYSTEM "../../dtd/dblite.dtd">
<!-- This chapter is copied over from the Subversion book and slightly
     modified for the TortoiseSVN client.
-->
<chapter id="tsvn-basics">
  <title>Basic Version-Control Concepts</title>
  <simplesect>
    <indexterm>
      <primary>Subversion book</primary>
    </indexterm>
    <para>
      This chapter is a slightly modified version of the same chapter
      in the Subversion book. An online version of the Subversion book is
      available here:
      <ulink url="https://svnbook.red-bean.com/">
        <citetitle>https://svnbook.red-bean.com/</citetitle>
      </ulink>.
    </para>
    <para>
      This chapter is a short, casual introduction to Subversion.
      If you're new to version control, this chapter is definitely for
      you. We begin with a discussion of general version control
      concepts, work our way into the specific ideas behind
      Subversion, and show some simple examples of Subversion in
      use.
    </para>
    <para>
      Even though the examples in this chapter show people sharing
      collections of program source code, keep in mind that Subversion
      can manage any sort of file collection - it's not limited to
      helping computer programmers.
    </para>
  </simplesect>
  <sect1 id="tsvn-basics-repository">
    <title>The Repository</title>
    <indexterm>
      <primary>repository</primary>
    </indexterm>
    <para>
      Subversion is a centralized system for sharing information.
      At its core is a <firstterm>repository</firstterm>, which is a
      central store of data. The repository stores information in the
      form of a <firstterm>filesystem tree</firstterm> - a typical
      hierarchy of files and directories. Any number of
      <firstterm>clients</firstterm> connect to the repository, and
      then read or write to these files. By writing data, a client
      makes the information available to others; by reading data, the
      client receives information from others.
    </para>
    <figure id="tsvn-basics-dia1">
      <title>A Typical Client/Server System</title>
      <graphic fileref="images/ch02dia1.png"/>
    </figure>
    <para>
      So why is this interesting? So far, this sounds like the
      definition of a typical file server. And indeed, the repository
      <emphasis>is</emphasis> a kind of file server, but it's not your
      usual breed. What makes the Subversion repository special is
      that <emphasis>it remembers every change</emphasis> ever written
      to it: every change to every file, and even changes to the
      directory tree itself, such as the addition, deletion, and
      rearrangement of files and directories.
    </para>
    <para>
      When a client reads data from the repository, it normally
      sees only the latest version of the filesystem tree. But the
      client also has the ability to view
      <emphasis>previous</emphasis> states of the filesystem. For
      example, a client can ask historical questions like, <quote>
        what did
        this directory contain last Wednesday?
      </quote>, or <quote>
        who was the last
        person to change this file, and what changes did they make?
      </quote>
      These are the sorts of questions that are at the heart of any
      <firstterm>version control system</firstterm>: systems that are
      designed to record and track changes to data over time.
    </para>
  </sect1>
  <!-- the philosophical section -->
  <sect1 id="tsvn-basics-versioning">
    <title>Versioning Models</title>
    <para>
      All version control systems have to solve the same
      fundamental problem: how will the system allow users to share
      information, but prevent them from accidentally stepping on
      each other's feet? It's all too easy for users to
      accidentally overwrite each other's changes in the
      repository.
    </para>
    <sect2 id="tsvn-basics-versioning-filesharing">
      <title>The Problem of File-Sharing</title>
      <para>
        Consider this scenario: suppose we have two co-workers,
        Harry and Sally. They each decide to edit the same repository
        file at the same time. If Harry saves his changes to the
        repository first, then it's possible that (a few moments
        later) Sally could accidentally overwrite them with her own
        new version of the file. While Harry's version of the file
        won't be lost forever (because the system remembers every
        change), any changes Harry made <emphasis>won't</emphasis> be
        present in Sally's newer version of the file, because she
        never saw Harry's changes to begin with. Harry's work is
        still effectively lost - or at least missing from the
        latest version of the file - and probably by accident.
        This is definitely a situation we want to avoid!
      </para>
      <figure id="tsvn-basics-dia2">
        <title>The Problem to Avoid</title>
        <graphic fileref="images/ch02dia2.png"/>
      </figure>
    </sect2>
    <sect2 id="tsvn-basics-versioning-lockmodifyunlock">
      <title>The Lock-Modify-Unlock Solution</title>
      <para>
        Many version control systems use a
        <firstterm>lock-modify-unlock</firstterm> model to address
        this problem, which is a very simple solution. In such a
        system, the repository allows only one person to change a file
        at a time. First Harry must <emphasis>lock</emphasis> the file before he can begin
        making changes to it. Locking a file is a lot like borrowing
        a book from the library; if Harry has locked a file, then Sally
        cannot make any changes to it. If she tries to lock the file,
        the repository will deny the request. All she can do is read
        the file, and wait for Harry to finish his changes and release
        his lock. After Harry unlocks the file, his turn is over, and
        now Sally can take her turn by locking and editing.
      </para>
      <figure id="tsvn-basics-dia3">
        <title>The Lock-Modify-Unlock Solution</title>
        <graphic fileref="images/ch02dia3.png"/>
      </figure>
      <para>
        The problem with the lock-modify-unlock model is that it's
        a bit restrictive, and often becomes a roadblock for
        users:
      </para>
      <itemizedlist>
        <listitem>
          <para>
            <emphasis>Locking may cause administrative problems.</emphasis>
            Sometimes Harry will lock a file and then forget about it.
            Meanwhile, because Sally is still waiting to edit the file,
            her hands are tied. And then Harry goes on vacation. Now
            Sally has to get an administrator to release Harry's lock.
            The situation ends up causing a lot of unnecessary delay
            and wasted time.
          </para>
        </listitem>
        <listitem>
          <para>
            <emphasis>Locking may cause unnecessary serialization.</emphasis>
            What if Harry is editing the beginning of a text file,
            and Sally simply wants to edit the end of the same file?
            These changes don't overlap at all. They could easily
            edit the file simultaneously, and no great harm would
            come, assuming the changes were properly merged together.
            There's no need for them to take turns in this
            situation.
          </para>
        </listitem>
        <listitem>
          <para>
            <emphasis>Locking may create a false sense of security.</emphasis>
            Pretend that Harry locks and edits file A, while
            Sally simultaneously locks and edits file B. But suppose
            that A and B depend on one another, and the changes made
            to each are semantically incompatible. Suddenly A and B
            don't work together anymore. The locking system was
            powerless to prevent the problem - yet it somehow
            provided a sense of false security. It's easy for Harry and
            Sally to imagine that by locking files, each is beginning a
            safe, insulated task, and thus inhibits them from
            discussing their incompatible changes early
            on.
          </para>
        </listitem>
      </itemizedlist>
    </sect2>
    <sect2 id="tsvn-basics-versioning-copymodifymerge">
      <title>The Copy-Modify-Merge Solution</title>
      <para>
        Subversion, CVS, and other version control systems use a
        <firstterm>copy-modify-merge</firstterm> model as an
        alternative to locking. In this model, each user's client
        reads the repository and creates a personal <firstterm>
          working
          copy
        </firstterm> of the file or project. Users then work in
        parallel, modifying their private copies. Finally, the
        private copies are merged together into a new, final version.
        The version control system often assists with the merging, but
        ultimately a human being is responsible for making it happen
        correctly.
      </para>
      <para>
        Here's an example. Say that Harry and Sally each create
        working copies of the same project, copied from the
        repository. They work concurrently, and make changes to the
        same file <filename>A</filename> within their copies. Sally saves her changes to
        the repository first. When Harry attempts to save his changes
        later, the repository informs him that his file A is
        <firstterm>out-of-date</firstterm>. In other words, that file
        A in the repository has somehow changed since he last copied
        it. So Harry asks his client to <firstterm>merge</firstterm>
        any new changes from the repository into his working copy of
        file A. Chances are that Sally's changes don't overlap with
        his own; so once he has both sets of changes integrated, he
        saves his working copy back to the repository.
      </para>
      <figure id="tsvn-basics-dia4">
        <title>The Copy-Modify-Merge Solution</title>
        <graphic fileref="images/ch02dia4.png"/>
      </figure>
      <figure id="tsvn-basics-dia5">
        <title>...Copy-Modify-Merge Continued</title>
        <graphic fileref="images/ch02dia5.png"/>
      </figure>
      <indexterm>
        <primary>conflict</primary>
      </indexterm>
      <para>
        But what if Sally's changes <emphasis>do</emphasis> overlap
        with Harry's changes? What then? This situation is called a
        <firstterm>conflict</firstterm>, and it's usually not much of
        a problem. When Harry asks his client to merge the latest
        repository changes into his working copy, his copy of file A
        is somehow flagged as being in a state of conflict: he'll be
        able to see both sets of conflicting changes, and manually
        choose between them. Note that software can't automatically
        resolve conflicts; only humans are capable of understanding
        and making the necessary intelligent choices. Once Harry has
        manually resolved the overlapping changes (perhaps by
        discussing the conflict with Sally!), he can safely save the
        merged file back to the repository.
      </para>
      <para>
        The copy-modify-merge model may sound a bit chaotic, but
        in practice, it runs extremely smoothly. Users can work in
        parallel, never waiting for one another. When they work on
        the same files, it turns out that most of their concurrent
        changes don't overlap at all; conflicts are infrequent. And
        the amount of time it takes to resolve conflicts is far less
        than the time lost by a locking system.
      </para>
      <para>
        In the end, it all comes down to one critical factor: user
        communication. When users communicate poorly, both syntactic
        and semantic conflicts increase. No system can force users to
        communicate perfectly, and no system can detect semantic
        conflicts. So there's no point in being lulled into a false
        promise that a locking system will somehow prevent conflicts;
        in practice, locking seems to inhibit productivity more than
        anything else.
      </para>
      <para>
        There is one common situation where the lock-modify-unlock
        model comes out better, and that is where you have unmergeable
        files. For example if your repository contains some graphic
        images, and two people change the image at the same time, there
        is no way for those changes to be merged together. Either Harry
        or Sally will lose their changes.
      </para>
    </sect2>
    <sect2 id="tsvn-basics-versioning-4">
      <title>What does Subversion Do?</title>
      <para>
        Subversion uses the copy-modify-merge solution by default,
        and in many cases this is all you will ever need. However,
        as of Version 1.2, Subversion also supports file locking,
        so if you have unmergeable files, or if you are simply
        forced into a locking policy by management, Subversion
        will still provide the features you need.
      </para>
    </sect2>
  </sect1>
  <!-- How svn implements the philosophy -->
  <sect1 id="tsvn-basics-svn">
    <title>Subversion in Action</title>
    <sect2 id="tsvn-basics-svn-workingcopy">
      <title>Working Copies</title>
      <indexterm>
        <primary>working copy</primary>
      </indexterm>
      <para>
        You've already read about working copies; now we'll
        demonstrate how the Subversion client creates and uses
        them.
      </para>
      <para>
        A Subversion working copy is an ordinary directory tree on
        your local system, containing a collection of files. You can
        edit these files however you wish, and if they're source code
        files, you can compile your program from them in the usual
        way. Your working copy is your own private work area:
        Subversion will never incorporate other people's changes, nor
        make your own changes available to others, until you
        explicitly tell it to do so.
      </para>
      <para>
        After you've made some changes to the files in your
        working copy and verified that they work properly, Subversion
        provides you with commands to <emphasis>publish</emphasis> your changes to the
        other people working with you on your project (by writing to
        the repository). If other people publish their own changes,
        Subversion provides you with commands to merge those changes
        into your working directory (by reading from the
        repository).
      </para>
      <para>
        A working copy also contains some extra files, created and
        maintained by Subversion, to help it carry out these commands.
        In particular, your working copy contains a
        subdirectory named <filename>.svn</filename>, also known as
        the working copy <firstterm>
          administrative
          directory
        </firstterm>. The files in this administrative
        directory help Subversion recognize which files contain
        unpublished changes, and which files are out-of-date with
        respect to others' work. Prior to 1.7 Subversion maintained
        <filename>.svn</filename> administrative subdirectories in every
        versioned directory of your working copy.
        Subversion 1.7 takes a completely different approach and each
        working copy now has only one administrative subdirectory which
        is an immediate child of the root of that working copy.
      </para>
      <para>
        A typical Subversion repository often holds the files (or
        source code) for several projects; usually, each project is a
        subdirectory in the repository's filesystem tree. In this
        arrangement, a user's working copy will usually correspond to
        a particular subtree of the repository.
      </para>
      <para>
        For example, suppose you have a repository that contains
        two software projects.
      </para>
      <figure id="tsvn-basics-dia6">
        <title>The Repository's Filesystem</title>
        <graphic fileref="images/ch02dia6.png"/>
      </figure>
      <para>
        In other words, the repository's root directory has two
        subdirectories: <filename>paint</filename> and
        <filename>calc</filename>.
      </para>
      <para>
        To get a working copy, you must <firstterm>
          check
          out
        </firstterm> some subtree of the repository. (The term
        <emphasis>check out</emphasis> may sound like it has something to do with locking
        or reserving resources, but it doesn't; it simply creates a
        private copy of the project for you.)
      </para>
      <para>
        Suppose you make changes to <filename>button.c</filename>.
        Since the <filename>.svn</filename> directory remembers the
        file's modification date and original contents, Subversion can
        tell that you've changed the file. However, Subversion does
        not make your changes public until you explicitly tell it to.
        The act of publishing your changes is more commonly known as
        <firstterm>committing</firstterm> (or <firstterm>
          checking
          in
        </firstterm>) changes to the repository.
      </para>
      <para>
        To publish your changes to others, you can use
        Subversion's <command>commit</command> command.
      </para>
      <para>
        Now your changes to <filename>button.c</filename> have
        been committed to the repository; if another user checks out a
        working copy of <filename>/calc</filename>, they will see
        your changes in the latest version of the file.
      </para>
      <para>
        Suppose you have a collaborator, Sally, who checked out a
        working copy of <filename>/calc</filename> at the same time
        you did. When you commit your change to
        <filename>button.c</filename>, Sally's working copy is left
        unchanged; Subversion only modifies working copies at the
        user's request.
      </para>
      <para>
        To bring her project up to date, Sally can ask
        Subversion to <firstterm>update</firstterm> her working copy,
        by using the Subversion <command>update</command> command.
        This will incorporate your changes into her working copy, as
        well as any others that have been committed since she checked
        it out.
      </para>
      <para>
        Note that Sally didn't need to
        specify which files to update; Subversion uses the information
        in the <filename>.svn</filename> directory, and further
        information in the repository, to decide which files need to
        be brought up to date.
      </para>
    </sect2>
    <sect2 id="tsvn-basics-svn-urls">
      <title>Repository URLs</title>
      <para>
        Subversion repositories can be accessed through many
        different methods - on local disk, or through various
        network protocols. A repository location, however, is
        always a URL. The URL schema indicates the access
        method:
      </para>
      <table id="tsvn-basics-svn-table-1">
        <title>Repository Access URLs</title>
        <tgroup cols="2">
          <colspec colnum="1" colwidth="2*"/>
          <colspec colnum="2" colwidth="5*"/>
          <thead>
            <row>
              <entry>Schema</entry>
              <entry>Access Method</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>
                <literal>file://</literal>
              </entry>
              <entry>
                Direct repository access on local or network drive.
              </entry>
            </row>
            <row>
              <entry>
                <literal>http://</literal>
              </entry>
              <entry>
                Access via WebDAV protocol to Subversion-aware Apache server.
              </entry>
            </row>
            <row>
              <entry>
                <literal>https://</literal>
              </entry>
              <entry>
                Same as <literal>http://</literal>, but with SSL encryption.
              </entry>
            </row>
            <row>
              <entry>
                <literal>svn://</literal>
              </entry>
              <entry>
                Unauthenticated TCP/IP access via custom protocol
                to a <literal>svnserve</literal> server.
              </entry>
            </row>
            <row>
              <entry>
                <literal>svn+ssh://</literal>
              </entry>
              <entry>
                authenticated, encrypted TCP/IP access via custom protocol
                to a <literal>svnserve</literal> server.
              </entry>
            </row>
          </tbody>
        </tgroup>
      </table>
      <para>
        For the most part, Subversion's URLs use the standard
        syntax, allowing for server names and port numbers to be
        specified as part of the URL.
        The <literal>file://</literal> access method is normally used
        for local access, although it can be used with UNC paths to
        a networked host. The URL therefore takes the form
        <systemitem class="url">file://hostname/path/to/repos</systemitem>. For the
        local machine, the <literal>hostname</literal> portion of the URL is required
        to be either absent or <literal>localhost</literal>. For
        this reason, local paths normally appear with three slashes,
        <systemitem class="url">file:///path/to/repos</systemitem>.
      </para>
      <para>
        Also, users of the <literal>file://</literal> scheme on
        Windows platforms will need to use an unofficially
        <quote>standard</quote> syntax for accessing repositories
        that are on the same machine, but on a different drive than
        the client's current working drive. Either of the two
        following URL path syntaxes will work where
        <literal>X</literal> is the drive on which the repository
        resides:
      </para>
      <screen>
file:///X:/path/to/repos
...
file:///X|/path/to/repos
...
      </screen>
      <para>
        Note that a URL uses ordinary slashes even though the native
        (non-URL) form of a path on Windows uses backslashes.
      </para>
      <para>
        You can access a FSFS repository via a network share, but this
        is <emphasis>not</emphasis> recommended for various reasons:
      </para>
      <itemizedlist>
        <listitem>
          <para>
            You are giving direct write access to all users, so they could
            accidentally delete or corrupt the repository file system.
          </para>
        </listitem>
        <listitem>
          <para>
            Not all network file sharing protocols support the locking that
            Subversion requires. One day you will find your repository
            has been subtly <emphasis>corrupted</emphasis>.
          </para>
        </listitem>
        <listitem>
          <para>
            You have to set the access permissions in just the right way.
            SAMBA is particularly difficult in this respect.
          </para>
        </listitem>
        <listitem>
          <para>
            If one person installs a newer version of the client which
            upgrades the repository format, then everyone else will be
            unable to access the repository until they also upgrade to the
            new client version.
          </para>
        </listitem>
      </itemizedlist>
    </sect2>
    <sect2 id="tsvn-basics-svn-revisions">
      <title>Revisions</title>
      <indexterm>
        <primary>revision</primary>
      </indexterm>
      <para>
        A <command>svn commit</command> operation can publish
        changes to any number of files and directories as a single
        atomic transaction. In your working copy, you can change
        files' contents, create, delete, rename and copy files and
        directories, and then commit the complete set of changes as a
        unit.
      </para>
      <para>
        In the repository, each commit is treated as an atomic
        transaction: either all the commits changes take place, or
        none of them take place. Subversion retains this
        atomicity in the face of program crashes, system crashes,
        network problems, and other users' actions.
      </para>
      <para>
        Each time the repository accepts a commit, this creates a
        new state of the filesystem tree, called a
        <firstterm>revision</firstterm>. Each revision is assigned a
        unique natural number, one greater than the number of the
        previous revision. The initial revision of a freshly created
        repository is numbered zero, and consists of nothing but an
        empty root directory.
      </para>
      <para>
        A nice way to visualize the repository is as a series of
        trees. Imagine an array of revision numbers, starting at 0,
        stretching from left to right. Each revision number has a
        filesystem tree hanging below it, and each tree is a
        <quote>snapshot</quote> of the way the repository looked after
        each commit.
      </para>
      <figure id="tsvn-basics-dia7">
        <title>The Repository</title>
        <graphic fileref="images/ch02dia7.png"/>
      </figure>
      <sidebar>
        <title>Global Revision Numbers</title>
        <para>
          Unlike those of many other version control systems,
          Subversion's revision numbers apply to <emphasis>
            entire
            trees
          </emphasis>, not individual files. Each revision
          number selects an entire tree, a particular state of the
          repository after some committed change. Another way to
          think about it is that revision N represents the state of
          the repository filesystem after the Nth commit. When a
          Subversion user talks about ``revision 5 of
          <filename>foo.c</filename>'', they really mean
          ``<filename>foo.c</filename> as it appears in revision 5.''
          Notice that in general, revisions N and M of a file do
          <emphasis>not</emphasis> necessarily differ!
        </para>
      </sidebar>
      <para>
        It's important to note that working copies do not always
        correspond to any single revision in the repository; they may
        contain files from several different revisions. For example,
        suppose you check out a working copy from a repository whose
        most recent revision is 4:
      </para>
      <screen>
calc/Makefile:4
integer.c:4
button.c:4
      </screen>
      <para>
        At the moment, this working directory corresponds exactly
        to revision 4 in the repository. However, suppose you make a
        change to <filename>button.c</filename>, and commit that
        change. Assuming no other commits have taken place, your
        commit will create revision 5 of the repository, and your
        working copy will now look like this:
      </para>
      <screen>
calc/Makefile:4
integer.c:4
button.c:5
      </screen>
      <para>
        Suppose that, at this point, Sally commits a change to
        <filename>integer.c</filename>, creating revision 6. If you
        use <command>svn update</command> to bring your working copy
        up to date, then it will look like this:
      </para>
      <screen>
calc/Makefile:6
integer.c:6
button.c:6
      </screen>
      <para>
        Sally's changes to <filename>integer.c</filename> will
        appear in your working copy, and your change will still be
        present in <filename>button.c</filename>. In this example,
        the text of <filename>Makefile</filename> is identical in
        revisions 4, 5, and 6, but Subversion will mark your working
        copy of <filename>Makefile</filename> with revision 6 to
        indicate that it is still current. So, after you do a clean
        update at the top of your working copy, it will generally
        correspond to exactly one revision in the repository.
      </para>
    </sect2>
    <sect2 id="tsvn-basics-svn-wcrepository">
      <title>How Working Copies Track the Repository</title>
      <para>
        For each file in a working directory, Subversion records
        two essential pieces of information in the
        <filename>.svn/</filename> administrative area:
      </para>
      <itemizedlist>
        <listitem>
          <para>
            what revision your working file is based on
            (this is called the file's <firstterm>
              working
              revision
            </firstterm>), and
          </para>
        </listitem>
        <listitem>
          <para>
            a timestamp recording when the local copy was
            last updated by the repository.
          </para>
        </listitem>
      </itemizedlist>
      <para>
        Given this information, by talking to the repository,
        Subversion can tell which of the following four states a
        working file is in:
      </para>
      <variablelist>
        <varlistentry>
          <term>Unchanged, and current</term>
          <listitem>
            <para>
              The file is unchanged in the working
              directory, and no changes to that file have been committed
              to the repository since its working revision. A
              <command>commit</command> of the file will do nothing,
              and an <command>update</command> of the file will do
              nothing.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>Locally changed, and current</term>
          <listitem>
            <para>
              The file has been changed in the working
              directory, and no changes to that file have been committed
              to the repository since its base revision. There are local
              changes that have not been committed to the repository, thus
              a <command>commit</command> of the file will succeed in
              publishing your changes, and an <command>update</command>
              of the file will do nothing.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>Unchanged, and out-of-date</term>
          <listitem>
            <para>
              The file has not been changed in the working
              directory, but it has been changed in the repository. The
              file should eventually be updated, to make it current with
              the public revision. A <command>commit</command> of the
              file will do nothing, and an <command>update</command> of
              the file will fold the latest changes into your working
              copy.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>Locally changed, and out-of-date</term>
          <listitem>
            <para>
              The file has been changed both in the
              working directory, and in the repository. A <command>commit</command>
              of the file will fail with an <emphasis>out-of-date</emphasis>
              error. The file should be updated first; an <command>update</command>
              command will attempt to merge the public
              changes with the local changes. If Subversion can't
              complete the merge in a plausible way automatically, it
              leaves it to the user to resolve the
              conflict.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </sect2>
  </sect1>
  <sect1 id="tsvn-basics-summary">
    <title>Summary</title>
    <para>
      We've covered a number of fundamental Subversion concepts in
      this chapter:
    </para>
    <itemizedlist>
      <listitem>
        <para>
          We've introduced the notions of the central repository,
          the client working copy, and the array of repository
          revision trees.
        </para>
      </listitem>
      <listitem>
        <para>
          We've seen some simple examples of how two collaborators
          can use Subversion to publish and receive changes from one
          another, using the 'copy-modify-merge' model.
        </para>
      </listitem>
      <listitem>
        <para>
          We've talked a bit about the way Subversion tracks and
          manages information in a working copy.
        </para>
      </listitem>
    </itemizedlist>
  </sect1>
</chapter>
<!--
local variables:
sgml-parent-document: ("book.xml" "chapter")
end:
-->
