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: There is at least one x_7 for which x_7 is not a janitor. For all x_7, x_7 is a janitor or x_7 is not an office clerk. For all x_7, x_7 is an office clerk or x_7 is not a janitor.
For all x_7, if x_7 were an office clerk, then x_7 is a janitor can be inferred via the universal rewriting rule. For all x_7, if x_7 were a janitor, then x_7 is an office clerk can be inferred via the universal rewriting rule.