report: add some references

doc/report/references.bib

@@ -44,4 +44,38 @@
     date = {2020},
     urldate = {2020-06-10},
     url = {http://graphdb.ontotext.com/documentation/free/using-graphdb-with-the-rdf4j-api.html},
-}
\ No newline at end of file
+}
+
+@inproceedings{ulo,
+    title={Relational data across mathematical libraries},
+    author={Condoluci, Andrea and Kohlhase, Michael and M{\"u}ller, Dennis and Rabe, Florian and Coen, Claudio Sacerdoti and Wenzel, Makarius},
+    booktitle={International Conference on Intelligent Computer Mathematics},
+    pages={61--76},
+    year={2019},
+    organization={Springer}
+}
+
+@online{tetra,
+    title={Towards a Heterogeneous Query Language for Mathematical Knowledge},
+    author={Bercic, Katja Kohlhase, Michael Rabe, Florian},
+    urldate = {2020-06-16},
+    url = {https://kwarc.info/people/mkohlhase/papers/cicm20-search.pdf},
+}
+
+@article{mmtbase,
+    title={Mathematical knowledge management: transcending the one-brain-barrier with theory graphs},
+    author={Kohlhase, Michael},
+    journal={European Mathematical Society (EMS) Newsletter},
+    volume={92},
+    pages={22--27},
+    year={2014}
+}
+
+@book{owl,
+    title={A semantic web primer},
+    author={Antoniou, Grigoris and Van Harmelen, Frank},
+    year={2004},
+    pages={113--152},
+    chapter={4},
+    publisher={MIT press}
+}