Robert Collier (2013). “The Secret of the Ages: The Secret Edition - Open Your Heart to the Real Power and Magic of Living Faith and Let the Heaven Be in You, Go Deep Inside Yourself and Back, Feel the Crazy and Divine Love and Live for Your Dreams”, p.14, Lulu Press, Inc
Joseph Murphy, Ph.D., D.D. (2009). “Putting the Power of Your Subconscious Mind to Work: Reach New Levels of Career Success Using the Power of Your Subconscious Mind”, p.6, Penguin