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_2, if x_2 were a nurse, then x_2 is working. There is at least one x_2 for which x_2 will not work. For all x_2, if x_2 writes a letter, then x_2 is a nurse.
There is at least one x_2 for which x_2 is not a nurse can be inferred via the existential modus tollens rule. For all x_2, if x_2 writes a letter, then x_2 is working can be inferred via the universal transitivity rule.