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: q_2 <-> p_7. p_18 <-> r_3. p_7 -> p_18. ~r_3.
q_2 -> p_7 can be inferred via the biconditional elimination rule. p_18 -> r_3 can be inferred via the biconditional elimination rule. p_7 -> q_2 can be inferred via the biconditional elimination rule. r_3 -> p_18 can be inferred via the biconditional elimination rule. ~p_18 can be inferred via the biconditional elimination rule.