* <a href="#type-comparator">comparator</a></span></code></div><div class="spec-doc"><p>Compare two subroutines by composition for an empty postcondition:</p><p>Given two subroutines and environments, return a postcondition and hypothesis that, when passed to <code>compare_subs</code>, will generate a precondition which is provable only if (modulo soundness bugs) the VCs generated by the hooks provided by the environment are satisfied.</p></div></div><div class="odoc-spec"><div class="spec value" id="val-co