Orthocentric Systems in Minkowski Planes
  A new way to define the notion of $\C$-orthocenter will be displayed by studying some propierties of four points in the plane which allows to extend the notion of Euler's line, the Six Point Circles and the three-circles theorem, for normed planes. In the present paper (which can be regarded as extention of \cite{M-WU} in Minkowski plane in general) we derive several characterizations of the Euclidianity of the plane. 
Wilson Pacheco Redondo and Tob\'ias Rosas Soto
math.MG