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_1, x_1 will write a letter or x_1 will take a plane. For all x_1, x_1 is not a musician. For all x_1, if x_1 writes a letter, then x_1 is a musician.
For all x_1, x_1 will not write a letter can be inferred via the universal modus tollens rule.