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. u_1 <-> r.
u_1 -> r can be inferred via the biconditional elimination rule. r -> u_1 can be inferred via the biconditional elimination rule. ~u_1 can be inferred via the biconditional elimination rule.