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 <-> r_1. p_18 <-> r. r -> s. w -> r_1.
p_18 -> r_1 can be inferred via the biconditional elimination rule. p_18 -> r can be inferred via the biconditional elimination rule. r_1 -> p_18 can be inferred via the biconditional elimination rule. r -> p_18 can be inferred via the biconditional elimination rule.