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_9. p_18 <-> r_1. ~p_18. p_9 <-> p_2.
~p_9 and ~p_18 can be inferred via the conjunction rule. ~p_18 and ~p_9 can be inferred via the conjunction rule. p_18 -> r_1 can be inferred via the biconditional elimination rule. p_9 -> p_2 can be inferred via the biconditional elimination rule. r_1 -> p_18 can be inferred via the biconditional elimination rule. p_2 -> p_9 can be inferred via the biconditional elimination rule. ~r_1 can be inferred via the biconditional elimination rule. ~p_2 can be inferred via the biconditional elimination rule.