diff --git a/bibliography.bib b/bibliography.bib
index 70ecfb35f34a69203ec2b0d7bba256d92faac278..ea3ddbfa8333f9dd8d40320cea63ac17ddab14c2 100644
--- a/bibliography.bib
+++ b/bibliography.bib
@@ -153,6 +153,42 @@
 }
 
 
+@inproceedings{Tao.662011682011,
+ author = {Tao, Long and Liu, Zhigang},
+ title = {Optimization on multi-robot workcell layout in vertical plane},
+ pages = {744--749},
+ publisher = {IEEE},
+ isbn = {978-1-4577-0268-6},
+ booktitle = {2011 IEEE International Conference on Information and Automation},
+ year = {6/6/2011 - 6/8/2011},
+ doi = {10.1109/ICINFA.2011.5949092}
+}
+
+
+@inproceedings{Vahrenkamp2013,
+ author = {Vahrenkamp, Nikolaus and Asfour, Tamim and Dillmann, Rudiger},
+ title = {Robot placement based on reachability inversion},
+ pages = {1970--1975},
+ publisher = {IEEE},
+ isbn = {978-1-4673-5643-5},
+ booktitle = {2013 IEEE International Conference on Robotics and Automation},
+ year = {5/6/2013 - 5/10/2013},
+ doi = {10.1109/ICRA.2013.6630839}
+}
+
+
+@misc{Wikipedia2021,
+ abstract = {Roll-Nick-Gier-Winkel, englisch roll-pitch-yaw angle, sind spezielle Eulerwinkel (Lagewinkel), die zur Beschreibung der Ausrichtung eines Fahrzeugs im dreidimensionalen Raum herangezogen werden. Diese Art der Richtungsmessung und -bestimmung durch Drehratensensoren wurde zur Navigation im Luftverkehr eingef{\"u}hrt und wird inzwischen neben Luftfahrzeugen auch f{\"u}r Raum-, Land- und Wasserfahrzeuge verwendet.},
+ editor = {Wikipedia},
+ year = {2021},
+ title = {Roll-Nick-Gier-Winkel},
+ url = {https://de.wikipedia.org/w/index.php?title=Roll-Nick-Gier-Winkel&oldid=209197743},
+ urldate = {7/11/2021},
+ doi = {Page},
+ file = {Roll-Nick-Gier-Winkel:Attachments/Roll-Nick-Gier-Winkel.pdf:application/pdf}
+}
+
+
 @inproceedings{Zacharias2007,
  author = {Zacharias, Franziska and Borst, Christoph and Hirzinger, Gerd},
  title = {Capturing robot workspace structure: representing robot capabilities},