Problems with the EFG formalism: a solution attempt using observations

Abstract: We argue that the extensive-form game (EFG) model isn't powerful enough to express all important aspects of imperfect information games, such as those related to decomposition and online game solving. We present a principled attempt to fix the formalism by considering information partitions that correspond to observations. We show that EFGs cannot be "fixed" without additional knowledge about the original task, and show how to extend the EFG model under this assumption. However, during our investigation, we ultimately concluded that a better solution is to abandon EFGs entirely and instead adopt a model based on partially observable stochastic games. The primary contribution of the text thus lies in exposing the problems with EFGs and presenting a detailed study on introducing imperfect information by adding observations into an underlying perfect-information model.