During the second half of the nineteenth century the pitch-class complex A-flat-C-E was regularly invoked by Liszt, Wagner, Strauss and Mahler in orchestral works dealing with spiritual redemption (Erlösung). The theme of metaphysical transfiguration, which continued to dominate Austro-German opera even after Wagner's death (contrary to Dahlhaus's claim of a retreat into sentimentality and Märchenoper), also played a considerable role in important orchestral music from the period. In addition to incorporating the clarifying device of a program, these works cite the A flat-C-E complex as a musical sign that redemption is at issue. While the associative meaning of the complex remained generally consistent, however, the associations of individual keys varied from composer to composer. Furthermore, works of Strauss (Also sprach Zarathustra, Tod und Verklärung, Till Eulenspiegels lustige Streiche) and Mahler (Symphonies Nos. 2 and 8) engage critically with the complex, identifying it as aesthetically outdated.