Petsche, Johanna J. M. 2015. Gurdjieff and Music: The Gurdjieff/de Hartmann Piano Music and its Esoteric Significance. Leiden and Boston, MA: Brill. xvi + 279pp. Ebook. US$130. E-ISBN: 9789004284449. Hbk. US$142.00. ISBN-13: 96789004284425