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. q_11. ~p_15 -> s_1. r_4 -> ~q_11. r_4 -> p_15.
~r_4 can be inferred via the modus tollens rule. p_15 -> ~q_11 can be inferred via the transitivity rule. p_15 <-> r_4 can be inferred via the biconditional introduction rule. r_4 <-> p_15 can be inferred via the biconditional introduction rule.