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_1 -> r_1. r_1 -> p_1. ~r_1. s_3 or p_1.
~p_1 can be inferred via the modus tollens rule. ~p_1 -> s_3 can be inferred via the rewriting rule. p_1 <-> r_1 can be inferred via the biconditional introduction rule. r_1 <-> p_1 can be inferred via the biconditional introduction rule.