What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? David is not reading a book. If David reads a book, then William is listening to a song. David is reading a book if and only if William is listening to a song.
If David reads a book, then William is listening to a song. If William listens to a song, then David is reading a book. William is not listening to a song.