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. u -> s. p <-> u. q -> u. s -> q.
~s can be inferred via the modus tollens rule. u -> q can be inferred via the transitivity rule. q -> s can be inferred via the transitivity rule. s -> u can be inferred via the transitivity rule. p -> u can be inferred via the biconditional elimination rule. u -> p can be inferred via the biconditional elimination rule.