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: ~s. ~t -> q_1. t <-> s. t -> s.
~t can be inferred via the modus tollens rule. t -> s can be inferred via the biconditional elimination rule. s -> t can be inferred via the biconditional elimination rule. ~t can be inferred via the biconditional elimination rule.