What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_5, if x_5 were sad, then x_5 is an astronaut. For all x_5, if x_5 were an astronaut, then x_5 is sad. For all x_5, if x_5 were a doctor, then x_5 is an astronaut.
For all x_5, if x_5 were a doctor, then x_5 is sad. For all x_5, x_5 is sad if and only if x_5 is an astronaut. For all x_5, x_5 is an astronaut if and only if x_5 is sad.