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 Robert listens to a song, then William is an astronaut. For all y, y will listen to a song or y will write a letter. William is an astronaut or Robert is not writing a letter.
If Robert writes a letter, then William is an astronaut can be inferred via the rewriting rule.