What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_13, x_13 is a cashier if and only if x_13 will write a letter. For all x_13, x_13 is a nurse. For all x_13, x_13 is a cashier or x_13 is not a nurse. For all x_13, if x_13 were a cashier, then x_13 is a janitor.
For all x_13, if x_13 were a nurse, then x_13 is a cashier. For all x_13, if x_13 were a cashier, then x_13 is writing a letter. For all x_13, if x_13 writes a letter, then x_13 is a cashier.