span></code>, the source abstract
        value <code class="computeroutput"><span class="identifier">N</span><span class="special">=</span><span class="identifier">abt</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>, a destination type <code class="computeroutput"><span class="identifier">T</span></code>;
        and whenever possible, a result typed value <code class="computeroutput"><span class="identifier">t</span></code>
        of type <code c