Book 1: https://books.apple.com/ch/book/flexible-guitar-duets-book-1/id6444201347?l=en
Book 2: https://books.apple.com/ch/book/flexible-guitar-duets-book-2/id6444202188?l=en
Book 3: https://books.apple.com/ch/book/flexible-guitar-duets-book-3/id6444202694?l=en
Book 4: https://books.apple.com/ch/book/flexible-guitar-duets-book-4/id6444236755?l=en
