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 were a janitor, then x_6 is climbing a mountain. For all x_6, x_6 is sad or x_6 is a janitor. For all x_6, x_6 is not sad. For all x_6, x_6 is a mechanic.
For all x_6, x_6 is a janitor can be inferred via the universal disjunctive syllogism rule.