Retrat del matemàtic danès Chistian Juel (1855-1935)
<bdi><a href="https://www.wikidata.org/wiki/Q427821" class="extiw" title="d:Q427821"><span title="Danish photographer (1833-1907)">Christian Neuhaus</span></a>
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MacTutor History of Mathematics: <a rel="nofollow" class="external free" href="http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Juel.html">http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Juel.html</a>