lass="pln"><span class="n"><a id="t173" href="#t173">173</a></span><span class="t">&nbsp;</span><span class="r"></span></p>
    <p class="pln"><span class="n"><a id="t174" href="#t174">174</a></span><span class="t">                        <span class="com"># Check which edges are "external" => next cell is wall</span>&nbsp;</span><span class="r"></span></p>
    <p class="pln"><span class="n"><a id="t175" href="#t175">175</a></span><span class="t">                        <span class="com"># edges in the orde