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_1 <-> s_1. s_1 or ~w_1.
w_1 -> s_1 can be inferred via the rewriting rule. w_1 -> s_1 can be inferred via the biconditional elimination rule. s_1 -> w_1 can be inferred via the biconditional elimination rule.