What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If John were sad, then David is an artist. Joseph is working if and only if David is an artist. John is sad if and only if Joseph is working.
If Joseph works, then David is an artist. If John were sad, then Joseph is working. If David were an artist, then Joseph is working. If Joseph works, then John is sad.