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, x_9 is a police officer if and only if x_9 is rich. For all x_9, x_9 is rich or x_9 is a taxi driver. For all x_9, if x_9 were a scientist, then x_9 is a police officer. There is at least one x_9 for which if x_9 were a taxi driver, then x_9 is a scientist.
There is at least one x_9 for which if x_9 were a taxi driver, then x_9 is a police officer can be inferred via the existential transitivity rule. For all x_9, if x_9 were a police officer, then x_9 is rich can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 were rich, then x_9 is a police officer can be inferred via the universal biconditional elimination rule.