s="org-ul">
<li>parser(generator(x)) = x
</li>
<li>generator(parser(x)) need not be x
</li>
<li>Semantics are preserved, syntax not necessarily
</li>
</ul>
</li>
</ul>
</section>
<section id="sec-7-2" >

<h3>Streams</h3>
<table><tr><td width="70%">

<ul class="org-ul">
<li>Existing parsers consume a single, implicit input stream
</li>
<li>Nail introduces multiple streams 
</li>
<li>Allows grammars to move between them
</li>
<li>We introduce transformations to create new streams
</li>
</ul>

</td><td>
<img s