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 primary 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.

Write the following queries in Relational Algebra:

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

2. 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).