What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Charles writes a letter, then Sarah is not driving a car. Elisabeth is sleeping. Barbara is working if and only if Charles is writing a letter. Sarah is driving a car.
Charles is not writing a letter. Elisabeth is sleeping and Sarah is driving a car. Sarah is driving a car and Elisabeth is sleeping. If Barbara works, then Charles is writing a letter. If Charles writes a letter, then Barbara is working.