an class="dv">1</span>]]),
                      <span class="dt">perpendicular =</span> <span class="kw">c</span>(M$Mr.perp[[<span class="dv">1</span>]], M$Ml.perp[[<span class="dv">1</span>]]),
                      <span class="dt">side =</span> <span class="kw">gl</span>(<span class="dv">2</span>, <span class="kw">length</span>(stack$angle),
                                <span class="dt">labels=</span><span class="kw">c</span>(<span class="st">"front"</span>, <span class="st">"back"</span>)))

## basi