and the expression <code class="computeroutput"><span class="identifier">p</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code>
        must be valid where <code class="computeroutput"><span class="identifier">p</span></code> is
        an object of type <code class="computeroutput"><span class="identifier">Predicate</span></code>,
        <code class="computeroutput"><span class="identifier">x</span></code> is an object of type <code class="computeroutp