er_kind"><span class="modifier"></span> <span class="kind">def</span></span> <span class="symbol"><span class="implicit">ensuring</span><span class="params">(<span name="cond">cond: (<a href="" name="provingground.translation.Statement.Definition" id="provingground.translation.Statement.Definition" class="extype">Definition</a>[<span name="provingground.translation.Statement.Definition.S" class="extype">S</span>, <span name="provingground.translation.Statement.Definition.E" class="extype">E</span>]) =&gt; <