Music for Piano 21

Analyzing Music for Piano 21, I notice that it includes an unplayable note
(D-flat above the highest C on the piano). It's very confusing to me,
because this is one Cage himself played with Tudor regularly; surely he
knew the note couldn't be played. What did he do? Are there any pianists on
the list who play this one and can tell me what they do?
Rob

-- 
Rob Haskins, D.M.A., Ph.D.
Associate Professor
Department of Music, College of Liberal Arts
University of New Hampshire
M-105, Paul Creative Arts Center
30 Academic Way
Durham, NH 03824
603-862-3987 (office)
603-862-3155 (fax)
<http://unh.edu/music/>
<http://robhaskins.net>
<http://musicandmiscellaneous.blogspot.com/>