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: ~r_4. u -> q_6. r_4 <-> r_6. q_6 -> r_6.
u -> r_6 can be inferred via the transitivity rule. r_4 -> r_6 can be inferred via the biconditional elimination rule. r_6 -> r_4 can be inferred via the biconditional elimination rule. ~r_6 can be inferred via the biconditional elimination rule.