instruction: What are the first names of all history professors who do not teach?
response: SELECT T1.emp_fname FROM employee AS T1 JOIN professor AS T2 ON T1.emp_num = T2.emp_num JOIN department AS T3 ON T2.dept_code = T3.dept_code WHERE T3.dept_name = 'History' EXCEPT SELECT T4.emp_fname FROM employee AS T4 JOIN class AS T5 ON T4.emp_num = T5.prof_num