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: David is playing a game if and only if Charles is playing tennis. If David plays a game, then Richard is a taxi driver. If James climbs a mountain, then Charles is playing tennis. If Richard were a taxi driver, then James is climbing a mountain.
If David plays a game, then James is climbing a mountain can be inferred via the transitivity rule. If Richard were a taxi driver, then Charles is playing tennis can be inferred via the transitivity rule. If David plays a game, then Charles is playing tennis can be inferred via the biconditional elimination rule. If Charles plays tennis, then David is playing a game can be inferred via the biconditional elimination rule.