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: ~u. p -> q_3. q_3 <-> u. q_3 -> p.
p <-> q_3 can be inferred via the biconditional introduction rule. q_3 <-> p can be inferred via the biconditional introduction rule. q_3 -> u can be inferred via the biconditional elimination rule. u -> q_3 can be inferred via the biconditional elimination rule. ~q_3 can be inferred via the biconditional elimination rule.