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