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 <-> q_21. ~p. u_2 -> p_17. p_17 <-> q_21.
p -> q_21 can be inferred via the biconditional elimination rule. p_17 -> q_21 can be inferred via the biconditional elimination rule. q_21 -> p can be inferred via the biconditional elimination rule. q_21 -> p_17 can be inferred via the biconditional elimination rule. ~q_21 can be inferred via the biconditional elimination rule.