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_15 <-> r_4. p_15 -> r_4. ~p_15 -> q. ~r_4.
~p_15 can be inferred via the modus tollens rule. p_15 -> r_4 can be inferred via the biconditional elimination rule. r_4 -> p_15 can be inferred via the biconditional elimination rule. ~p_15 can be inferred via the biconditional elimination rule.