Example A. Bartok, “Free Variations” from Mikrokosmos, Vol. 6
What pitch source is used in example A (above)?
For further study of twentieth-century compositional techniques, see:
Kostka, Stephan and Dorothy Payne. Tonal Harmony: With an Introduction to Twentieth-Century Music. 5th edition. McGraw-Hill, 2004. (Specifically Chapter 28)
For more in-depth and complete coverage of twentieth-century compositional techniques, see the following resources:
Kostka, Stephan. Materials and Techniques of Twentieth-Century Music. 2nd edition. Prentice Hall, 1990.
Straus, Joseph N. Introduction to Post-Tonal Theory. 3rd edition. Pearson Prentice Hall, 2005.