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_9 <-> r. p <-> r. ~p_9.
p_9 -> r can be inferred via the biconditional elimination rule. p -> r can be inferred via the biconditional elimination rule. r -> p_9 can be inferred via the biconditional elimination rule. r -> p can be inferred via the biconditional elimination rule. ~r can be inferred via the biconditional elimination rule.