This is the closing sequence of Valve's Portal, in 6502 assembly language,
as displayed by an Apple II computer.
This is a follow-on to the Portal in Applesoft BASIC
project I did a few years ago. I was never satisfied with the beeper music at
the end, so this version has either 4-channels of AY-3-8910 audio
(if you have a Mockingboard card) or 2-channels of
beeper sound if you don't.
The first half is the 80col/Mockingboard version, the second half
is the 40col/Electric Duet version.
The letter 'Z' does not appear at all in the lyrics to the song.
(Noticed when I had an off-by one error in the uppercasing code).