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, z will drink water or z is an astronaut. For all z, if z were an astronaut, then z is a police officer. For all z, if z drinks water, then z is a police officer. There is at least one z for which if z were a police officer, then z is drinking water.
There is at least one z for which if z were an astronaut, then z is drinking water can be inferred via the existential transitivity rule. For all z, z is a police officer can be inferred via the universal disjunction elimination rule. There is at least one z for which z is a police officer if and only if z will drink water can be inferred via the existential biconditional introduction rule. There is at least one z for which z will drink water if and only if z is a police officer can be inferred via the existential biconditional introduction rule.