Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE employee ( emp_fname VARCHAR, emp_jobcode VARCHAR )
TABLE: CREATE TABLE CLASS ( prof_num VARCHAR )

### Question ###
What are the first names of the professors who do not teach a class.

### Accurate SQL ###

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