This appears to reference Terry Riley's In C: > In C consists of 53 short, numbered musical phrases, lasting from half a beat to 32 beats; each phrase may be r

This appears to reference Terry Riley's In C: > In C consists of 53 short, numbered musical phrases, lasting from half a beat to 32 beats; each phrase may be repeated an arbitrary number of times. Each musician has control over which phrase they play: players are encouraged to play the phrases starting at different times, even if they are playing the same phrase. (https://en.m.wikipedia.org/wiki/In_C https://en.m.wikipedia.org/wiki/In_C)