 Complete the following phrase:  Since the mid-1950s, Stockhausen had been developing concepts of spatialization in his works, not only in electronic music, such as the 5-channel Gesang der Jünglinge 195556 and Telemusik 1966, and 4-channel Kontakte 195860 and Hymnen 196667. Instrumentalvocal works like Gruppen for three orchestras 195557 and Carré for four orchestras and four choirs 195960 also exhibit this trait. In lectures such as Music in Space from 1958, he called for new kinds of concert halls to be built, suited to the requirements of spatial music. His idea was In 1968, the West German government invited Stockhausen to collaborate on the German Pavilion at the 