What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_8, if x_8 takes a plane, then x_8 is listening to a song. For all x_8, if x_8 listens to a song, then x_8 is taking a plane. Robert is not taking a plane. Robert is listening to a song or Joseph is reading a book.
For all x_8, x_8 will take a plane if and only if x_8 will listen to a song. For all x_8, x_8 will listen to a song if and only if x_8 will take a plane.