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: q -> w. w -> q. q -> w.
q <-> w can be inferred via the biconditional introduction rule. w <-> q can be inferred via the biconditional introduction rule. w <-> q can be inferred via the biconditional introduction rule. q <-> w can be inferred via the biconditional introduction rule.