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: p_2 <-> r. r <-> p_2.
p_2 -> r can be inferred via the biconditional elimination rule. r -> p_2 can be inferred via the biconditional elimination rule. r -> p_2 can be inferred via the biconditional elimination rule. p_2 -> r can be inferred via the biconditional elimination rule.