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. ~r. q.
~r and q can be inferred via the conjunction rule. q and ~r can be inferred via the conjunction rule. u -> r can be inferred via the biconditional elimination rule. r -> u can be inferred via the biconditional elimination rule. ~u can be inferred via the biconditional elimination rule.