Let A be the set of students at your school and B the set of books in the school library. Let R1 and R2 be the relations consisting of all ordered pairs (a, b), where student a is required to read book b in a course, and where student a has read book b, respectively. Describe the ordered pairs in each of these relations.
a) R1 ∪ R2
b) R1 ∩ R2
c) R1 ⊕ R2
d) R1 − R2
e) R2 − R1