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_1 <-> q. q -> s. t -> s_1. s -> t. ~s_1.
~t can be inferred via the modus tollens rule. q -> t can be inferred via the transitivity rule. s -> s_1 can be inferred via the transitivity rule. s_1 -> q can be inferred via the biconditional elimination rule. q -> s_1 can be inferred via the biconditional elimination rule. ~q can be inferred via the biconditional elimination rule.