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: p_15 -> s_4. ~w_4. w_4 <-> s_4. s_4 -> p_15.
p_15 <-> s_4 can be inferred via the biconditional introduction rule. s_4 <-> p_15 can be inferred via the biconditional introduction rule. w_4 -> s_4 can be inferred via the biconditional elimination rule. s_4 -> w_4 can be inferred via the biconditional elimination rule. ~s_4 can be inferred via the biconditional elimination rule.