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: For all x_3, if x_3 plays a game, then x_3 is climbing a mountain. For all x_3, if x_3 plays a game, then x_3 is climbing a mountain. For all x_3, if x_3 climbs a mountain, then x_3 is playing a game.
For all x_3, x_3 will play a game if and only if x_3 will climb a mountain can be inferred via the universal biconditional introduction rule. For all x_3, x_3 will play a game if and only if x_3 will climb a mountain can be inferred via the universal biconditional introduction rule. For all x_3, x_3 will climb a mountain if and only if x_3 will play a game can be inferred via the universal biconditional introduction rule. For all x_3, x_3 will climb a mountain if and only if x_3 will play a game can be inferred via the universal biconditional introduction rule.