Boston: Allyn & Bacon, Inc. (1969): 114, Example 8-11; 116, Example 8-18; 117, Example 8-20.
Boston: Allyn & Bacon, Inc. (1969): 114, De Exemplu 8-11; 116, Exemplu 8-18; 117, De Exemplu 8-20. ^ Bussler, Ludwig (1890).