Merge two references in line 43 of our paper as suggested by reviewer Marcel Stimberg.

Author: jhstaudacher

paper/paper.md

@@ -57,7 +57,7 @@ One problem of using computational models in research, is their oftentimes limit
 ## What is a Public Goods Game
 The tragedy of the commons describes an important social and economical phenomenon which pitches self interest against the interests of a group. Players in a Public Goods Game (PGG) can either contribute to a common pool (cooperate) or withhold their contribution (defect). The money collected in the pool is increased by a multiplicative synergy factor, and then equally distributed amongst the players. It becomes immediately clear that the defecting players will always receive the same as the cooperators, but end up having more money than the cooperators due to the amount they withheld before. The tragedy specifically describes the dilemma, that if all players would cooperate the total amount received by everyone would be higher, but the greed (or self interest) of the defectors prevents that favourable outcome.
 
-The question is how to overcome the tragedy of the commons. In social societies, often institutions, regulations, and incentives are used [@fehr2002altruistic], [@hintze2020inclusive]. In the theoretical context, all of this becomes abstracted as costly punishment [@hardin1968tragedy]. This costly punishment has been shown to affect human behavior [@fehr2002altruistic] and can indeed lead to the evolution of cooperation [@hintze2015punishment]. Another option that alters the outcome towards cooperation could be asymmetric distribution of resources, as it can be found in many animal hierarchies. Hyenas for example have a steep despotic index [@smith2007rank] while also cooperating with each other, supporting the idea of asymmetric payoffs potentially leading to cooperation.
+The question is how to overcome the tragedy of the commons. In social societies, often institutions, regulations, and incentives are used [@fehr2002altruistic; @hintze2020inclusive]. In the theoretical context, all of this becomes abstracted as costly punishment [@hardin1968tragedy]. This costly punishment has been shown to affect human behavior [@fehr2002altruistic] and can indeed lead to the evolution of cooperation [@hintze2015punishment]. Another option that alters the outcome towards cooperation could be asymmetric distribution of resources, as it can be found in many animal hierarchies. Hyenas for example have a steep despotic index [@smith2007rank] while also cooperating with each other, supporting the idea of asymmetric payoffs potentially leading to cooperation.
 
 ## Statement of Need
 Studying evolution in a biological systems is cumbersome, to say the least [@lenski2017experimental]. Consequently, using computational models becomes a viable alternative. However, for new experiments to build on previous results, the modeling software needs to be extendable. This leads to a challenging problem. Future users will independently modify the software to suit their own needs, with no regard for other users. This could create an ever growing tree of alternative versions, that might not be compatible with each other. Here, a modular design (see \autoref{fig:Classes}) approach is used, such that possible future users can define custom modules. However, those modules will remain interoperable, because interfaces are well defined.