<p>This was a tough call.</p>

<p>CW tends to be used here for questions likely to generate useful and interesting replies, but where no single objectively best reply seems possible.  It might also be applied to questions of a rapidly evolving nature (if such questions are deemed so important that they shouldn't be closed).</p>

<p>In the case of the arXiv question, it was posed in a way that at least seemed to allow the possibility of a unique objectively valid answer that would be permanently useful.  (Nevertheless, when I first saw it I paused over the "close" button for a long time.)  I was delighted that several such answers have since appeared, differing only in the evidence they use to support their common conclusion.</p>
