"New Shapes for Shells" (1961) Bulletin of the International Association for Shell Structures, No. 8: pp. 123-130, as quoted by , "39 etc… : Heinz Isler’s infinite spectrum of new shapes for shells" (2009) Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia, Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures, 28 September – 2 October 2009, Universidad Politecnica de Valencia, Spain, eds. , Carlos Lazhttps://en.wikiquote.org/wiki/Heinz_Isler