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: For all x_19, x_19 will read a book. If Robert were an artist, then Jennifer is taking a plane. For all x_19, if x_19 takes a plane, then x_19 is not a janitor. For all x_19, if x_19 reads a book, then x_19 is a janitor. Susan is a writer.
For all x_19, x_19 is a janitor can be inferred via the universal modus ponens rule.