You need to describe the library model. There are 3 entities: "Author", "Book", "Reader" -- Physically, there is only one book and it can only be with one reader. You need to create tables for the library to reflect this. -- A book can have multiple authors.

To describe the library model considering the conditions, the following tables can be used:

1. Authors:

• id (PK)
• name

2. Books:

• id (PK)
• title
• reader_id (FK, nullable) — indicates the reader who currently owns the book; null if the book is available

3. Readers:

• id (PK)
• name

4. BookAuthors (many-to-many relationship between books and authors):

• book_id (FK)
• author_id (FK)

Features:

• A book physically exists and can be owned by one reader, so the reader_id field in the Books table stores the current owner.
• To link multiple authors to a single book, an intermediate table BookAuthors is used.

This design ensures:

• Tracking the current owner of the book (one reader per book).
• The relationship of a book with multiple authors.