ber of operands is less than 2. This may improve sharing, but also improves compatibility of smtlib2 expressions with other solvers.</p></div></div><div class="odoc-spec"><div class="spec value" id="val-check_external" class="anchored"><a href="#val-check_external" class="anchor"></a><code><span><span class="keyword">val</span> check_external : 
  <span><span class="xref-unresolved">Z3</span>.Solver.solver <span class="arrow">&#45;&gt;</span></span>
  <span>string <span class="arrow">&#45;&gt;</span></span>