BOOK(isbn, title, num-pages, publisher, year, genre, price, aut-id). The first attribute is the primary key; the last one is a foreign key to AUTHOR. CUSTOMER(customer-id, name, address, city, state, zip, age). The first attribute is the pri- mary key. SALES(isbn, custid, num-copies, day, month, year, total). The first attribute is a foreign key to BOOK and the second a foreign key to CUSTOMER. The key of this table is the two foreign keys together. AUTHOR(author-id, name, dob, nationality, address, city, state, zip). The first attribute is the primary key.

DO NOT GIVE ANSWER THAT HAS SQL, ONLY RELATIONAL ALGEBRA

7. List the name and address of authors who have written at least two books.

8. List the name and address of authors who have written only sci-fi books (i.e. all the books they have written are sci-fi).