scissa values: that's exactly what happens if we perform
        argument substitution, replacing <code class="computeroutput"><span class="identifier">x</span></code>
        by <code class="computeroutput"><span class="identifier">exp</span><span class="special">(-</span><span class="identifier">x</span><span class="special">)</span></code> (note
        that we must also multiply by the derivative of <code class="computeroutput"><span class="identifier">exp</span><span class="special">(-</span><span clas