In a letter to Russell Fritz (as known as Ron Franz), April 1992 in "Back to the Wild" by Chris McCandless and Mary Ellen Barnes, (2nd ed.), Twin Star Press, (pp. 135-137), 2013.
Henry David Thoreau, Laura Ross (2009). “Walden, Or, Life in the Woods: Bold-faced Ideas for Living a Truly Transcendent Life”, p.273, Sterling Publishing Company, Inc.