What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all z, if z were a taxi driver, then z is drinking water. For all z, if z drinks water, then z is a taxi driver. There is at least one z for which z will drink water if and only if z will write a letter. For all z, z will not write a letter.
For all z, z is a taxi driver if and only if z will drink water. For all z, z will drink water if and only if z is a taxi driver. There is at least one z for which if z drinks water, then z is writing a letter. There is at least one z for which if z writes a letter, then z is drinking water. There is at least one z for which z will not drink water.