Karlheinz Stockhausen,.. "Helikopter-Streichquartett", Grand Street 14, no. 4 (Spring 1996, "Grand Street 56: Dreams"): 213–225. ISBN1-885490-07-0. Online variant version [1999], as "Introduction: Helicopter String Quartet (1992/93)" (some omissions, some supplements, different illustrations; archive from 17 November 2014, accessed 11 August 2016).