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 will take a plane if and only if x_13 is sad. For all x_13, x_13 is a janitor. For all x_13, if x_13 were a janitor, then x_13 is taking a plane. For all x_13, x_13 is sad if and only if x_13 will work.
For all x_13, x_13 will take a plane. For all x_13, if x_13 takes a plane, then x_13 is sad. For all x_13, if x_13 were sad, then x_13 is working. For all x_13, if x_13 were sad, then x_13 is taking a plane. For all x_13, if x_13 works, then x_13 is sad.