of_item</span>:<span>(<span><a href="../Item/index.html#type-t">Item.t</a> <span class="arrow">&#45;&gt;</span></span> <a href="../../CostDomain/BasicCost/index.html#type-t">BasicCost.t</a>)</span> <span class="arrow">&#45;&gt;</span></span>
  <span><a href="#type-t">t</a> <span class="arrow">&#45;&gt;</span></span>
  unit</span></code></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-improve_cost_with"><a href="#val-improve_cost_with" class="anchor"></a><code><span><span class="ke