anchor.diff:  ./main.native</pre>
             <p>This should display <code>Hello world!</code> on the terminal.</p>
   
  -          <h2>More examples</h2>
  +          <h2 id="examples">More examples</h2>
             <p>The full documentation of the <a href="https://github.com/coq-io/system"><code>coq:io:system</code></a> library is available on <a href="http://coq-io.github.io/doc/system/2.3.0/toc.html">v2.3.0</a>.</p>
   
             <h3>Your name</h3>
  
positive.code:   end.</pre>
            <p>We use the function <code>System.eval</code> to evaluate a command and get its status code and output. If the two <code>uname</code> calls are successful, we retrieve the OS and machine names and display them. The <code>0%Z</code> stands for the zero in the type <code>Z</code> of the relative integers. A null value means by convention that the commands were successful.</p>
  
            <h2>Use concurrency</h2>
            <p>In order not to freeze, interactive programs usually need to run many IO operations in parallel. Consider for example an application which must keep a reactive user interface while doing slow network operations.</p>
            <p>To run two operations in parallel, we use the <code>join</code> operator:</p>
            <pre>join : C.t E A -> C.t E B -> C.t E (A * B)</pre>
  
negative.code:       <div class="row">
          <div class="col-md-12">
            <h1>Getting started</h1>
            <ul>
              <li><a href="#hello-world">Write a Hello World</a></li>
              <li><a href="#examples">More examples</a></li>
              <li><a href="#concurrency">Use concurrency</a></li>
              <li><a href="#effects">The effects system</a></li>
              <li><a href="#use-cases">Verification by use cases</a></li>
            </ul>
            <p>To install the <a href="http://coq.io/">Coq.io</a> library, enable the <a href="https://github.com/coq/repo-stable">repo-stable</a> OPAM repository and run:</p>
            <pre>opam install -j4 -v coq:io:system</pre>
            This will install the main library <a href="https://github.com/coq-io/io"><code>coq:io</code></a> and some basic effects <a href="https://github.com/coq-io/system"><code>coq:io:system</code></a> to interact with your operating system.
  
            <h2 id="hello-world">Write a Hello World</h2>
            Open your favorite <a href="https://coq.inria.fr/">Coq</a> editor and type:
            <pre>Require Import Coq.Lists.List.
  Require Import Io.All.
  