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: ~w. u_3 -> r_3. w <-> u_3. r_3 -> u_3.
u_3 <-> r_3 can be inferred via the biconditional introduction rule. r_3 <-> u_3 can be inferred via the biconditional introduction rule. w -> u_3 can be inferred via the biconditional elimination rule. u_3 -> w can be inferred via the biconditional elimination rule. ~u_3 can be inferred via the biconditional elimination rule.