The term "four-part harmony" refers to music written for four voices or for some other musical medium—four musical instruments or a single keyboard instrument, for example—where the various musical parts can give a different note for each chord of the music.
Music is a collection of sounds.
Music is a collection of different sounds, however it usually refers a collection of different sounds arranged in a melodic, harmonious way. The system was fooled by this because it was not considering the definition of music in the original statement.
( z1 collect :ARG1 ( z2 sound ) :domain ( z3 music ) )