4.8 as discussed in section 4.4.8, we expect the constraint "an instructor cannot teach sections in two different classrooms in a semester in the same time slot" to hold. a. write an sql query that returns all (instructor, section) combinations that violate this constraint. b. write an sql assertion to enforce this constraint (as discussed in section 4.4.8, current generation database systems do not support such assertions, although they are part of the sql standard).