If you are looking for the sheet music for György Ligeti's Piano Études
Contains Études 15–18 (with the final one left somewhat isolated as the series concluded). UNT Digital Library Key Musical & Analytical Concepts
High-energy, award-winning (Grawemeyer 1986). Focuses on "disorder" and extreme technical demands. Désordre, Fanfares, Arc-en-ciel Book 2 (7–14)