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: For all z_3, z_3 is fast or z_3 is not a bartender. There is at least one z_3 for which z_3 is fast if and only if z_3 is a bartender.
For all z_3, if z_3 were a bartender, then z_3 is fast can be inferred via the universal rewriting rule. There is at least one z_3 for which if z_3 were fast, then z_3 is a bartender can be inferred via the existential biconditional elimination rule. There is at least one z_3 for which if z_3 were a bartender, then z_3 is fast can be inferred via the existential biconditional elimination rule.