What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Richard listens to a song, then Richard is writing a letter. For all x, if x writes a letter, then x is listening to a song. For all x, if x listens to a song, then x is writing a letter.
For all x, x will write a letter if and only if x will listen to a song. For all x, x will listen to a song if and only if x will write a letter.