The reversed Cauchy inequality is another consequence of the convexity of either light cone. For two distinct similarly directed time-like vectors u 1 and u 2 this inequality is η η ( u 1 , u 2 ) > ‖ u 1 ‖ ‖ u 2 ‖ or algebraically, c 2 t 1 t 2 − − x 1 x 2 − − y 1 y 2 − − z 1 z 2 > ( c 2 t 1 2 − − x 1 2 − − y 1 2 − − z 1 2 ) ( c 2 t 2 2 − − x 2 2 − − y 2 2 − − z 2 2 )