Charles Sanders Peirce (1933). “Collected Papers of Charles Sanders Peirce: Exact logic (Published papers).. The Simplest mathematics”, Harvard University Press
Charles Sanders Peirce, Nathan Houser, Christian J.W. J. W. Kloesel (1992). “The Essential Peirce, Volume 1: Selected Philosophical Writings? (1867–1893)”, p.122, Indiana University Press
Charles Sanders Peirce, Nathan Houser, Christian J.W. J. W. Kloesel (1992). “The Essential Peirce, Volume 1: Selected Philosophical Writings? (1867–1893)”, p.149, Indiana University Press