What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: If David takes a plane, then Susan is a janitor. Richard is a musician. Robert is climbing a mountain or David is taking a plane. If Robert climbs a mountain, then Susan is a janitor. If Richard were a musician, then Michael is playing a game.
Michael is playing a game can be inferred via the modus ponens rule. Susan is a janitor can be inferred via the disjunction elimination rule.