Update publication list

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@@ -34,6 +34,15 @@
       <a href="https://ag-gipp.github.io/bib/preprints/greinerpetter2019.pdf">Preprint</a> 
       <a href="https://www.emeraldinsight.com/action/showCitFormats?doi=10.1108%2FAJIM-08-2018-0185">Bibtex</a>
    </li>
+   <li>
+      <strong>Towards Formula Concept Discovery and Recognition</strong>
+      <br/>P Scharpf, M Schubotz, HS Cohl, B Gipp<br/>
+      <em>Proceedings of the 4th Joint Workshop on Bibliometric-enhanced Information Retrieval and Natural Language Processing for Digital Libraries (BIRNDL 2019) co-located with the 42nd International ACM SIGIR Conference on Research and Development in Information Retrieval (SIGIR 2019), Paris, France, July 25, 2019.</em>
+      <br/>
+      <a href="http://ceur-ws.org/Vol-2414/paper11.pdf">PDF</a> 
+      <a href="http://ceur-ws.org/Vol-2414/paper11.pdf">Preprint</a> 
+      <a href="https://dblp.org/rec/bib/conf/sigir/ScharpfSCG19">Bibtex</a>
+   </li>
    <li>
       <strong>Four decades of TeX at zbMATH.</strong>
       <br/>M Schubotz, O Teschke<br/>