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_18 <-> w_1. t -> p_18. ~w_1. t or ~t_4.
t_4 -> t can be inferred via the rewriting rule. p_18 -> w_1 can be inferred via the biconditional elimination rule. w_1 -> p_18 can be inferred via the biconditional elimination rule. ~p_18 can be inferred via the biconditional elimination rule.