What is the first name of the professor who is teaching CIS-220 and QM-261?
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'
first name of the professor refers to emp_fname; teaching CIS-220 and QM-261 involves a relational JOIN between employee and class tables and an INTERSECT condition for the courses 'CIS-220' and 'QM-261';