ref="#cb6-8" aria-hidden="true" tabindex="-1"></a>    <span class="dt">real</span> delta = product &lt; <span class="dv">0</span> || (product == <span class="dv">0</span> &amp;&amp; (z1 + z2) &lt; <span class="dv">0</span>);</span>
<span id="cb6-9"><a href="#cb6-9" aria-hidden="true" tabindex="-1"></a>    <span class="cf">return</span> <span class="fl">0.5</span> * (Phi(z1) + Phi(z2) - delta)</span>
<span id="cb6-10"><a href="#cb6-10" aria-hidden="true" tabindex="-1"></a>                 - owens_t(z1, a1) -