Merge pull request #1249 from Axelrod-Python/marcharper-patch-1

Update citations.md

Author: meatballs

citations.md

@@ -1,15 +1,19 @@
 # Citations
 
-### 2018
+### 2019
+
+* Wang, Shiheng, and Fangzhen Lin. "Invincible Strategies of Iterated Prisoner's Dilemma." Proceedings of the 18th International Conference on Autonomous Agents and MultiAgent Systems. International Foundation for Autonomous Agents and Multiagent Systems, 2019.  [ArXiv](https://arxiv.org/abs/1712.06488)
+* Knight, Vincent A., et al. "Recognising and evaluating the effectiveness of extortion in the Iterated Prisoner's Dilemma." arXiv preprint arXiv:1904.00973 (2019). [ArXiv](https://arxiv.org/abs/1904.00973)
 
-* Goodman, Aaron. "Learning Implicit Communication Strategies for the Purpose of Illicit Collusion." arXiv preprint arXiv:1802.06036 (2018). [ArXiv](https://arxiv.org/abs/1802.06036)
+### 2018
+* Garcia, Julian, and Matthijs van Veelen. "No strategy can win in the repeated prisoner’s dilemma: Linking game theory and computer simulations." Frontiers in Robotics and AI 5.102 (2018) [pdf](https://static1.squarespace.com/static/56d27a10b6aa606b54a190bf/t/5b864ef11ae6cf2ee0c6c207/1535528708649/20.pdf)
+* Goodman, Aaron. "Learning multiagent coordination in the absence of communication channels." arXiv:1802.06036 (2018). [ArXiv](https://arxiv.org/abs/1802.06036)
 * Knight, Vincent, et al. "Evolution Reinforces Cooperation with the Emergence of Self-Recognition Mechanisms: an empirical study of the Moran process for the iterated Prisoner's dilemma."  PLoS ONE 13(10) (2018): e0204981. [PLOS](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0204981)
-* Latorre, Julian F. and Ospina, Juan Pablo and Ortiz, Jorge E.. "A Coalitional Game for Achieving Emergent Cooperation in Ad Hoc Networks Through Sympathy and Commitment." Springer (2018). [Springer](https://link.springer.com/chapter/10.1007/978-3-030-00350-0_30)
+* Latorre, Julian F. and Ospina, Juan Pablo and Ortiz, Jorge E. "A Coalitional Game for Achieving Emergent Cooperation in Ad Hoc Networks Through Sympathy and Commitment." Springer (2018). [Springer](https://link.springer.com/chapter/10.1007/978-3-030-00350-0_30)
 * Moura, Jose, and David Hutchison. "Game Theory for Multi-Access Edge Computing: Survey, Use Cases, and Future Trends." IEEE Communications Surveys & Tutorials (2018). [IEEE CS&T](https://ieeexplore.ieee.org/abstract/document/8424815) [ArXiv](https://arxiv.org/abs/1704.00323)
 * Neumann, Shai and Sood, Suraj and Hollander, Markus et al. "Using Bots in Strategizing Group Compositions to Improve Decision--Making Processes" Springer (2018). [Springer](https://link.springer.com/chapter/10.1007/978-3-319-91467-1_24)
 * Nicolas, Anastassacos and Mirco, Musolesi. "Learning through Probing: a decentralized reinforcement learning architecture for social dilemmas."arXiv preprint arXiv:1809.10007 (2018). [ArXiv](https://arxiv.org/abs/1809.10007)
 * Skiba, Grażyna, et al. "Flexible asynchronous simulation of iterated prisoner’s dilemma based on actor model." Simulation Modelling Practice and Theory 83 (2018): 75-92.
-* Wang, Shiheng, and Fangzhen Lin. "Invincible Strategies of Iterated Prisoner's Dilemma." arXiv preprint arXiv:1712.06488 (2017). [ArXiv](https://arxiv.org/abs/1712.06488)
 
 ### 2017