What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? James is a bartender if and only if David is a writer. If James were a bartender, then Barbara is a lawyer. If Mary were an artist, then Barbara is a lawyer. David is a writer.
If James were a bartender, then David is a writer. If David were a writer, then James is a bartender.