SELECT emp_fname FROM employee WHERE emp_jobcode  =  'PROF' EXCEPT SELECT T1.emp_fname FROM employee AS T1 JOIN CLASS AS T2 ON T1.emp_num  =  T2.prof_num
What are the first names of the professors who do not teach a class.
SELECT emp_fname FROM employee WHERE emp_jobcode = 'PROF ' EXCEPT SELECT T1.emp_fname FROM employee AS T1 JOIN CLASS AS T2 ON T1.emp_num = T2.prof_num
select emp_fname from employee where emp_jobcode = value except select t1 . emp_fname from employee as t1 join class as t2 on t1 . emp_num = t2 . prof_num
What are the first names of the professors who do not teach a class .