What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_4, x_4 is not an astronaut. For all x_4, if x_4 were an astronaut, then x_4 is a mechanic. For all x_4, if x_4 were an astronaut, then x_4 is a mechanic. There is at least one x_4 for which if x_4 were a mechanic, then x_4 is an astronaut.
There is at least one x_4 for which x_4 is not a mechanic. There is at least one x_4 for which x_4 is a mechanic if and only if x_4 is an astronaut. There is at least one x_4 for which x_4 is a mechanic if and only if x_4 is an astronaut. There is at least one x_4 for which x_4 is an astronaut if and only if x_4 is a mechanic. There is at least one x_4 for which x_4 is an astronaut if and only if x_4 is a mechanic.