Hi guys, i'm reading a book where the author, only form the invariance of the speed c draws conclusions about the transoformation from a system to another in inertial motion. The author shows a spacetime diagram (x,t) and the two dimensional light cone, he marks two events on the light cone (x1,t) and (-x1,t) and another event (0,t). He says since the three events are equally spaced in the first system and the transformation is linear they must be equally spaced also in the new system, why he assumes this? (the book still did not explained the invariance of the Minkwosky Norm), my brain is freezed now. Summing up the question: why he assumes that equally spaced events in a system must be equally spaced in another? thanks!