What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_11, x_11 is a taxi driver if and only if x_11 will climb a mountain. If Charles were a taxi driver, then Charles is climbing a mountain.
For all x_11, if x_11 were a taxi driver, then x_11 is climbing a mountain. For all x_11, if x_11 climbs a mountain, then x_11 is a taxi driver.