* {{cite book | last=Shirley | first=John | title=Gurdjieff: an introduction to his life and ideas | publisher=J.P. Tarcher/Penguin | publication-place=New York | date=2004 | isbn=1-58542-287-8}}
<ref name="q622">{{cite book | last=Shirley | first=John | title=Gurdjieff: an introduction to his life and ideas | publisher=J.P. Tarcher/Penguin | publication-place=New York | date=2004 | isbn=1-58542-287-8 | page=}}</ref>