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: w -> q_4. q_4 -> u_4. t <-> r_15. ~t. u_4 -> r_15.
q_4 -> r_15 can be inferred via the transitivity rule. t -> r_15 can be inferred via the biconditional elimination rule. r_15 -> t can be inferred via the biconditional elimination rule. ~r_15 can be inferred via the biconditional elimination rule.