What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_21, x_21 is not sad. If William were a lawyer, then John is reading a book. If Jennifer were sad, then Susan is a taxi driver. If Susan were a taxi driver, then Jennifer is sad. If John reads a book, then Susan is a taxi driver.
If William were a lawyer, then Susan is a taxi driver.