What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? James is a politician. If David reads a book, then James is a politician. James is a politician if and only if Robert is an artist. If Robert were an artist, then David is reading a book.
If Robert were an artist, then James is a politician. If James were a politician, then Robert is an artist. If Robert were an artist, then James is a politician.