Midterm 2015 Winter
4. a. Stores(sid, _, _) is not necessary
4. d. Answer should be 
∃a, s, c, g1, g2, n1, n2. Stores(s, n, c) ∧
(∀b1, b2. Catalog(s, b1) ∧ Catalog(s, b2) ->  Books(b1, n1, a, g1) ∧ Books(b2, n2, a, g2))

Midterm 2016 Winter
3. e. Correct answer should be (a).