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. q_3 <-> r_1. r <-> q_3. r -> ~u.
~r can be inferred via the modus tollens rule. q_3 -> r_1 can be inferred via the biconditional elimination rule. r -> q_3 can be inferred via the biconditional elimination rule. r_1 -> q_3 can be inferred via the biconditional elimination rule. q_3 -> r can be inferred via the biconditional elimination rule.