The checks in this lab also compare the column names.

1. ρ staff(staff_id, staff_name, dept, pay) (instructor)
2. ρ course_list(code, name) (π course_id, title (course))
3. How many tuples does ρ teacher (instructor) return?
4. σ pay > 90000 (ρ staff(staff_id, staff_name, dept, pay) (instructor))