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_6 -> ~u_1. u -> q_6. q_6 -> u. u_1.
~q_6 can be inferred via the modus tollens rule. u -> ~u_1 can be inferred via the transitivity rule. u <-> q_6 can be inferred via the biconditional introduction rule. q_6 <-> u can be inferred via the biconditional introduction rule.