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 sad, then x_18 is a mechanic. For all x_18, x_18 is a carpenter or x_18 is sad. There is at least one x_18 for which if x_18 were a carpenter, then x_18 is a mechanic. For all x_18, x_18 is an astronaut.
There is at least one x_18 for which x_18 is a mechanic.