(prime? (<span class="fu">+</span> (<span class="fu">car</span> pair) (<span class="fu">cadr</span> pair))))
 int-pairs)</code></pre>
<ul>
<li>We need some way of producing a stream of all integer pairs.</li>
<li>More generally, we can combined two streams to get a two-dimensional grid of pairs, and we want to reduce this to a one-dimensional stream.</li>
<li>One way to do this is to use <code>interleave</code> in the recursive definition, in order to handle infinite streams.</li>
</ul>
<aside><h4>Exercises