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: s_3. p_7 -> ~s_3. p_7 <-> r_4. t -> r_4.
~p_7 can be inferred via the modus tollens rule. p_7 -> r_4 can be inferred via the biconditional elimination rule. r_4 -> p_7 can be inferred via the biconditional elimination rule.