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_6, if x_6 writes a letter, then x_6 is playing a game. For all x_6, x_6 will write a letter or x_6 is a scientist. For all x_6, x_6 will not play a game.
For all x_6, x_6 will not write a letter can be inferred via the universal modus tollens rule.