="op">:</span><span class="fl">2</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="va">s1</span> <span class="op">+</span> <span class="va">s2</span>     <span class="co"># same as s1 | s2 or c(c1, s2)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span> {1, (1L 2L), 2}</span>
<span class="r-in"><span><span class="va">s2</span> <span class="op">+</span> <span class="va">s1</span>     <span class="co"># same</span></span></span>
<span class="r-out co">