Frank says:

I was writing all kinds of positive and negative canons and weird inverted this and retrograde that and getting as spaced-out mathematically as I could and I was going "Wait a minute (laughs), who cares about that stuff?" I had always liked rhythm and blues so here I was stuck between the slide rule and the gut bucket somewhere and I decided that I would opt for a third road someplace in between. -- From an 1972 interview to Martin Perlich. On giving up writing serial music.