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: u_4 <-> r_1. ~r_1.
u_4 -> r_1 can be inferred via the biconditional elimination rule. r_1 -> u_4 can be inferred via the biconditional elimination rule. ~u_4 can be inferred via the biconditional elimination rule.