Consider a database consisting of the following relations:

SAILORS(Sid, Sname, Rating, Age)

RESERVED(Sid, Bid, Day)

BOATS(Bid, Bname, Color)

For each of the following retrieval requests, write a relational algebra expression.

1. Retrieve the names of the sailors who have reserved a red or green boat.

2. Retrieve the names of the sailors with age over 20 who have not reserved a red boat.

3. Retrieve the names of the sailors who have reserved all boats.

4. Retrieve the color of the boat reserved by Smith.