1. Cayley, A.: Developments on the porism of the in-and-circumscribed polygon. Philos. Mag. 7, 339–345 (1854)
2. Coolidge, J.L.: A treatise on the circle and the sphere. Chelsea Publishing Co, Bronx (1971). (Reprint of the 1916 edition)
3. Coxeter, H.S.M.: Introduction to geometry. Wiley Classics Library. Wiley, New York (1989). (Reprint of the 1969 edition)
4. Culver, W.J.: On the existence and uniqueness of the real logarithm of a matrix. Proc. Am. Math. Soc. 17, 1146–1151 (1966)
5. Clark K.: Encyclopedia of Triangle Centers. http://faculty.evansville.edu/ck6/encyclopedia/etcpart3.html . Accessed 18 Dec 2017