What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Elisabeth takes a plane, then John is working. James is sad if and only if John is working. James is not sad. Joseph is a mechanic if and only if Elisabeth is taking a plane.
If James were sad, then John is working. If Joseph were a mechanic, then Elisabeth is taking a plane. If John works, then James is sad. If Elisabeth takes a plane, then Joseph is a mechanic. John is not working.