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_13, if x_13 reads a book, then x_13 is an office clerk. For all x_13, x_13 will climb a mountain or x_13 will read a book. For all x_13, if x_13 climbs a mountain, then x_13 is an office clerk. If John were a doctor, then Barbara is not an office clerk.
For all x_13, x_13 is an office clerk can be inferred via the universal disjunction elimination rule.