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
What are the first names of all history professors who do not teach?
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
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 = value except select t4 . emp_fname from employee as t4 join class as t5 on t4 . emp_num = t5 . prof_num
What are the first names of all history professors who do not teach ?