"US Open 2014 – Roger Federer: 'The difference between 142mph and 147mph, there's none really. Once you pass the 135 everything is just really fast'". www.ubitennis.net. August 30, 2014.
Sylvia Boorstein, Ph.D. (2007). “Pay Attention, for Goodness' Sake: Practicing the Perfections of the Heart--The Buddhist Path of Kindness”, p.20, Ballantine Books