Question: Find the first name of the professor who is teaching two courses with code CIS-220 and QM-261.
SQL: SELECT T1.emp_fname FROM employee AS T1 JOIN CLASS AS T2 ON T1.emp_num  =  T2.prof_num WHERE crs_code  =  'CIS-220' INTERSECT SELECT T1.emp_fname FROM employee AS T1 JOIN CLASS AS T2 ON T1.emp_num  =  T2.prof_num WHERE crs_code  =  'QM-261'