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 reads a book, then z is climbing a mountain. Elisabeth is not a taxi driver. David is climbing a mountain if and only if Elisabeth is a taxi driver.
If David climbs a mountain, then Elisabeth is a taxi driver. If Elisabeth were a taxi driver, then David is climbing a mountain. David is not climbing a mountain.