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 -> r. w_4 <-> s_1. t <-> r. ~t.
w_4 -> s_1 can be inferred via the biconditional elimination rule. t -> r can be inferred via the biconditional elimination rule. s_1 -> w_4 can be inferred via the biconditional elimination rule. r -> t can be inferred via the biconditional elimination rule. ~r can be inferred via the biconditional elimination rule.