  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.
