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_1 -> w. u_1 -> w. w -> u_1.
u_1 <-> w can be inferred via the biconditional introduction rule. u_1 <-> w can be inferred via the biconditional introduction rule. w <-> u_1 can be inferred via the biconditional introduction rule. w <-> u_1 can be inferred via the biconditional introduction rule.