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_4, if x_4 works, then x_4 is sad. For all x_4, x_4 will drink water or x_4 will work. For all x_4, if x_4 drinks water, then x_4 is sad. There is at least one x_4 for which x_4 is a politician.
For all x_4, x_4 is sad can be inferred via the universal disjunction elimination rule.