CREATE TABLE CLASS (prof_num VARCHAR)
CREATE TABLE employee (emp_fname VARCHAR, emp_num VARCHAR)

Find the first name of the professor who is teaching two courses with code 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'
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'