 In the extensive form games of  Section 2.1,  players move in sequence and can base their decisions on full information of what has happened so far. The other extreme were games in strategic form, where agents move in parallel or, in the interpretation of strategy selection, have no means of picking up information during actual play. There are ample scenarios in between these extremes. Public good games with optional retribution against non-cooperators (Andrighetto et al. 2013), for instance, combine moments where some or all players make simultaneous moves with information collection along the way. Such parallel action can be mimicked in sequential games by limiting the information available to players at various states of the game. The resulting games of imperfect information will be discussed in  Section 3,  alongside other sources of imperfect information.