1. Lecture Notes in Artificial Intelligence;M. Keeler,2000
2. Vehkavarra, T.: Peirce’s Classification of the Sciences,
http://mtlserver.uta.fi/~attove/peirce_systems3.pdf
3. Ransdell, J.M.: Arisbe, a philosophical website, providing coordinated access to the internet resources relevant to the life and work of, and continuing interest in the American philosopher, scientist, and humanist, Charles Sanders Peirce,
www.door.net/arisbe
4. See the Peirce Edition Project,
http://www.iupui.edu/~peirce
5. Meyers, R.G.: Peirce’s Extension of Empiricism. Transactions of the Charles S. Peirce Society XXXVIII(1/2), 137–154 (Winter/Spring 2002)