attribute type of <code class="computeroutput"><span class="identifier">b</span></code>,
            then the attribute type of <code class="computeroutput"><span class="identifier">a</span>
            <span class="special">&gt;&gt;</span> <span class="identifier">b</span></code>
            (<code class="computeroutput"><span class="identifier">a</span> <span class="special">&lt;&lt;</span>
            <span class="identifier">b</span></code>) will be <code class="computeroutput"><span class="identifier">