Le Deux Machina is a nearly 6 minute piano song by Mike Garson, a few seconds of it was used in Glass + The Ghost Children. A full synth version of this can be found on Machina II. And a full piano version can be found on a bootleg called Friends and Enemies of Modern Music (not to be confused with Machina II)
https://primanota.net/smashing-pumpkins/le-deux-machina-synth-lyrics.htm