  [,1] [,2]</span></span>
<span><span class="co">#  [1,]    1    3</span></span>
<span><span class="co">#  attr(,"class")</span></span>
<span><span class="co">#  [1] "XY"    "POINT" "sfg"</span></span>
<span><span class="co">## single-row matrix</span></span>
<span><span class="fu">a_point</span><span class="op">(</span> <span class="fu"><a href="https://rdrr.io/r/base/matrix.html" class="external-link">matrix</a></span><span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/c.html" class=