Progressive Elementary Solos and Duets Ernest S. Williams’ “Progressive Elementary Solos and Duets” is a must-have for private instructors and beginner players. This book gradually introduces players to the most important things to learn, including melody, harmony, counterpoint, and different keys. The music in this book progressively challenges the student’s physical abilities on the instrument, while stimulating them musically and creatively. Take a look at the free sample pages provided, and then place an order to have a book sent directly to your door.