All the other tones in the music fall 'between the cracks' of the piano keyboard -- off the grid of 12-tone equal temperament." In order to accomplish this, many of the musicians were aided by iPhones hooked up to either their instruments or their music rack so that technology could inform them exactly what pitch they were playing and the required timing of each note.
Practically, Chow delightfully spread the pages of Ligeti's demanding, poly-everything score across the music rack on a poster-sized sheet of pink oak tag and proceeded to attack this vivacious set of fanfares with infectious enthusiasm.
Pianists typically play solo literature with the music rack down and ensemble literature with the music rack up, which changes the amount of sound heard coming back in the hall, often causing pianists to play louder.
(And in this connection, I should add that with a minimum of effort even the rather hefty volume of overtures could be made to lie flat and stay open on the music rack.) It brought back fond memories of my college days and those many occasions when my roommate and I would repair to the senior common room after dinner to entertain ourselves with all manner of four-hand arrangements, which filled the piano bench and were piled high on the adjacent windowsill.