Abstract. A Minkowski geometry is Euclidean if and only if the altitudes of any trigon are concurrent. A Minkowski geometry is Euclidean if and only if the perpendicular bisectors of any trigon are concurrent.
AMS Subject Classification
(1991): 53A35; 51M09, 52A20
Received February 24, 2015, and in revised form March 26, 2015. (Registered under 18/2015.)