What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_9, if x_9 were a nurse, then x_9 is taking a plane. For all x_9, if x_9 takes a plane, then x_9 is a nurse. There is at least one x_9 for which if x_9 takes a plane, then x_9 is not writing a letter. For all x_9, x_9 will write a letter.
There is at least one x_9 for which x_9 will not take a plane. For all x_9, x_9 is a nurse if and only if x_9 will take a plane. For all x_9, x_9 will take a plane if and only if x_9 is a nurse.