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: ~t. q_19 <-> s. t <-> q_19. u -> s.
q_19 -> s can be inferred via the biconditional elimination rule. t -> q_19 can be inferred via the biconditional elimination rule. s -> q_19 can be inferred via the biconditional elimination rule. q_19 -> t can be inferred via the biconditional elimination rule. ~q_19 can be inferred via the biconditional elimination rule.