 These are particularly associated with the Cologne School and include such figures as Walter Zimmermann , Johannes Fritsch, Ladislav Kupkovič, Péter Eötvös, Bojidar Dino, Daniel Chorzempa, John McGuire, Mesías Maiguashca, and Clarence Barlow , as well as others from different countries such as Christopher Fox, Gerald Barry, Gavin Bryars, and Kevin Volans (; ).Most of these composers tend to use quite sparse, pared-down musical material (sometimes showing the influence of the early 'naive' period of work from John Cage, and that of Morton Feldman, especially in the case of Zimmermann) to which are applied more intricate musical processes; in the latter respect, the influence of Stockhausen and Mauricio Kagel is clear, though some of the figures concerned believed their aesthetic to constitute a break with the avant-garde as represented in particular at Darmstadt.In the United States and the Americas composers like Samuel Barber, Miguel del Aguila and Astor Piazzolla challenged the concept of music as an experiment with works that became instantly popular and remained in the classical music repertoire to this day.