@Q:
RETURN APPEND([ <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span> ], [ <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">2</span>, <span class="hljs-number">9</span> ], <span class="hljs-literal">true</span>)

@R
[
  [
    <span class="hljs-number">1</span>,
    <span class="hljs-number">2</span>,
    <span class="hljs-number">3</span>,
    <span class="hljs-number">4</span>,
    <span class="hljs-number">5</span>,
    <span class="hljs-number">9</span>
  ]
]