Kimberling, C. "Central Points and Central Lines in the Plane of a Triangle." Math. Mag.67, 163-187, 1994.Kimberling,
C. "Triangle Centers and Central Triangles." Congr. Numer.129,
1-295, 1998.Kimberling, C. "Encyclopedia of Triangle Centers: X(19)=Clawson
Point." http://faculty.evansville.edu/ck6/encyclopedia/ETC.html#X19.Lyness,
R. and Veldkamp, G. R. Problem 682 and Solution. Crux Math.9,
23-24, 1983.