Hauer's compositional techniques are extraordinarily various and often change from one piece to the next. These range from building-block techniques to methods using a chord series that is generated out of the twelve-tone row ("Melos") to pieces employing an ordered row that is then subject to systematic permutation. The so-called 44 "tropes" and their compositional usage ("trope-technique") are essential to many of Hauer's twelve-tone techniques. In contrast to a twelve-tone row that contains a fixed succession of twelve tones, a trope consists of two complementary hexachords in which there is no fixed tone sequence. The tropes are used for structural and intervallic views on the twelve-tone system. Every trope offers certain symmetries that can be used by the composer. But Hauer also employed twelve-tone rows, using one row for a single piece and subjecting that row to a series of transformations, most notably rotation (keeping the order of the elements in a series fixed but reorganizing them so that they start somewhere in the middle and wrap back around to the beginning: A B C D . . . becomes C D . . . A B, for instance.