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_5, if x_5 were a writer, then x_5 is a doctor. For all x_5, x_5 will sleep. For all x_5, x_5 will write a letter or x_5 is a writer. For all x_5, if x_5 writes a letter, then x_5 is a doctor.
For all x_5, x_5 is a doctor can be inferred via the universal disjunction elimination rule.