What does Observation mean? Why does the RL-Glue not use states?
If the state of an environment is fully observable, then you can often use the terms state and observation interchangeably. However, observation is a more general term that is meant to mean the perceptions that the agent receives. This can be different from the concept of state, which corresponds to some truth about the environment. For example, in partially observable environments, the observations may be aliased: the environment may be in different states, but the agent receives the same observation.
