What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If David were a nurse, then it is late. If William were a mechanic, then David is a nurse. If it is late, then Susan is a janitor. If Susan were a janitor, then William is a mechanic.
If David were a nurse, then Susan is a janitor. If William were a mechanic, then it is late. If it is late, then William is a mechanic. If Susan were a janitor, then David is a nurse.