identifier">Y</span></code> is not subranged, but the opposite <code class="computeroutput"><span class="special">(</span><span class="identifier">Y</span><span class="special">-&gt;</span><span class="identifier">X</span><span class="special">)</span></code> is,
        so that the supertype is always <code class="computeroutput"><span class="identifier">Y</span></code>,
        it is said that the direction <code class="computeroutput"><span class="identifier">X</span><span class="special">-&gt;</span><sp