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. r -> p_13. p_13 <-> u. r <-> q.
p_13 -> u can be inferred via the biconditional elimination rule. r -> q can be inferred via the biconditional elimination rule. u -> p_13 can be inferred via the biconditional elimination rule. q -> r can be inferred via the biconditional elimination rule. ~p_13 can be inferred via the biconditional elimination rule.