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: r_1 -> r_6. s_4 or w. r_6 <-> s_4. w <-> r_1.
r_6 -> s_4 can be inferred via the biconditional elimination rule. w -> r_1 can be inferred via the biconditional elimination rule. s_4 -> r_6 can be inferred via the biconditional elimination rule. r_1 -> w can be inferred via the biconditional elimination rule.