Shao-Cheng Liu, A Generalization of Th\'ebault's Theorem on
the Concurrency of Three Euler Lines,
Forum Geometricorum, 8 (2008) 205--208.
Abstract: We prove a generalization of Victor Th\'ebault's theorem that if
H_aH_bH_c is the orthic triangle of ABC, then the Euler lines of triangles
AH_cH_b, BH_aH_c, and CH_bH_a are concurrent at the center of the Jerabek
hyperbola which is the isogonal tranform of the Euler line.