thus the caller has top cost, then</p><p>1. if for callee, <code>top_pname_opt</code> is <code>None</code>, then callee is itself top cost, so for the caller, we record <code>top_pname_opt = callee</code> ;</p><p>2. if for callee, <code>top_pname_opt</code> is <code>f</code>, then we know that callee calls <code>f</code>, which is top cost, so for the caller, we record <code>top_pname_opt = f</code></p></header><div class="odoc-content"><div class="odoc-spec"><div class="spec type anchored" id="type-t"><a h