Paul Brody, Kenneth Grahame (2015). “The Life and Works of Kenneth Grahame: A Biography and Collection of Grahame’s Work”, p.332, BookCaps Study Guides
Louis O. Kelso, Patricia Hetter Kelso (1967). “Two-factor Theory: the Economics of Reality; how to Turn Eighty Million Workers Into Capitalists on Borrowed Money, and Other Proposals”, New York : Vintage Books