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_num VARCHAR)
TABLE: CREATE TABLE CLASS (prof_num VARCHAR)

### Question ###
Find the first names of professors who are teaching more than one class.

### Accurate SQL ###

SELECT T2.emp_fname FROM CLASS AS T1 JOIN employee AS T2 ON T1.prof_num = T2.emp_num GROUP BY T1.prof_num HAVING COUNT(*) > 1