Most generally complementation is the separation of pitch-class collections into two complementary sets, one containing the pitch classes not in the other [REF].
The term, "'combinatorial' appears to have been first applied to twelve-tone music by Milton Babbitt" in 1950,[REF] when he published a review of René Leibowitz's books Schoenberg et son école and Qu'est ce qu la musique de douze sons?[REF] Babbitt also introduced the term derived row [REF].