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_9, if x_9 were a scientist, then x_9 is not a taxi driver. For all x_9, x_9 is sad. For all x_9, x_9 is a taxi driver. For all x_9, x_9 is a scientist or x_9 is a poet.
For all x_9, x_9 is not a scientist can be inferred via the universal modus tollens rule. For all x_9, x_9 is sad and x_9 is a taxi driver can be inferred via the universal conjunction rule. For all x_9, x_9 is a taxi driver and x_9 is sad can be inferred via the universal conjunction rule.