Dr. Robert C. Worstell, Dorothea Brande, Claude M. Bristol, Earl Nightingale, Napoleon Hill (2017). “Mindset StackingTM Inspirational Journal VolumeSS01”, Lulu.com
Dr. Robert C. Worstell, James Breckenridge Jones, Napoleon Hill (2015). “Think and Grow Rich, Updated and Complete - With If You Can Count to Four...”, p.32, Lulu.com