Complex sentence: After 1940, Hauer wrote exclusively "Zwölftonspiele" ("Twelve-tone Games " or"Twelve-tone Playing"), designated sometimes by number, sometimes by date; he wrote about one thousand such pieces, most of them lost.
Split into simpler sentences: After 1940, Hauer wrote exclusively "Zwölftonspiele" ("Twelve-tone Games " or"Twelve-tone Playing"), designated sometimes by number, sometimes by date. He wrote about one thousand such pieces, most of them lost.