" title="Struct template concept_interface">concept_interface</a> can be specialized for either primitive or composite concepts. If a concept <code class="computeroutput">C1</code> contains another concept <code class="computeroutput">C2</code>, then the library guarantees that the specialization of <a class="link" href="concept_interface.html" title="Struct template concept_interface">concept_interface</a> for <code class="computeroutput">C2</code> is a base class of the specialization for <code class="com