er">sph_poly</span><span class="special">;</span>
    <span class="identifier">bg</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span><span class="string">"POLYGON((0 0,0 45,45 0,0 0))"</span><span class="special">,</span> <span class="identifier">sph_poly</span><span class="special">);</span>
    <span class="identifier">area</span> <span class="special">=</span> <span class="identifier">bg</span><span class="special">::</span><span class="identifier">