What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: If Richard were a taxi driver, then it is sunny. If Richard listens to a song, then it is sunny. Charles is climbing a mountain. For all y_3, y_3 is a taxi driver or y_3 will listen to a song.
Nothing can be inferred from these premises.