What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_18, if x_18 were an astronaut, then x_18 is sleeping. For all x_18, if x_18 sleeps, then x_18 is an astronaut. There is at least one x_18 for which if x_18 were a musician, then x_18 is writing a letter. For all x_18, x_18 is a scientist or x_18 is a musician. For all x_18, if x_18 were a scientist, then x_18 is writing a letter. For all x_18, if x_18 were an astronaut, then x_18 is not writing a letter.
There is at least one x_18 for which x_18 will write a letter. For all x_18, x_18 is an astronaut if and only if x_18 will sleep. For all x_18, x_18 will sleep if and only if x_18 is an astronaut.