Stanislav Grof, Hal Zina Bennett (2009). “The Holotropic Mind: The Three Levels of Human Consciousness and How They Shape Our Lives”, p.18, Harper Collins
Richard Pascale, Jerry Sternin, Monique Sternin (2013). “The Power of Positive Deviance: How Unlikely Innovators Solve the World's Toughest Problems”, p.120, Harvard Business Press