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_9, if x_9 were a writer, then x_9 is not writing a letter. For all x_9, x_9 is a writer or x_9 will take a plane. For all x_9, x_9 will work. For all x_9, x_9 will write a letter.
For all x_9, x_9 is not a writer can be inferred via the universal modus tollens rule. For all x_9, x_9 will work and x_9 will write a letter can be inferred via the universal conjunction rule. For all x_9, x_9 will write a letter and x_9 will work can be inferred via the universal conjunction rule.