What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Elisabeth is writing a letter if and only if Richard is a police officer. Elisabeth is writing a letter if and only if Richard is a police officer.
If Elisabeth writes a letter, then Richard is a police officer. If Elisabeth writes a letter, then Richard is a police officer. If Richard were a police officer, then Elisabeth is writing a letter. If Richard were a police officer, then Elisabeth is writing a letter.