For an infinite group, the derived series need not terminate at a finite stage, and one can continue it to infinite ordinal numbers via transfinite recursion, thereby obtaining the "'transfinite derived series "', which eventually terminates at the perfect core of the group.
12.
He also points to a " verifiable " pensato " " in the last bar of Alban Berg's " Lyric Suite " : " The instruments drop out one by one, the four parts converging into a single line that continues into an " ostinato " on the last two notes of the derived series and becomes inaudible on the penultimate note of the series, seemingly continuing into the silence beyond . " ( Perle, 1985)
