What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? David is playing a game if and only if Charles is excited. For all x_10, if x_10 takes a plane, then x_10 is playing a game. Charles is not excited.
If David plays a game, then Charles is excited. If Charles were excited, then David is playing a game. David is not playing a game.