in other words, if a mass m is at rest or is moving with constant acceleration (the constant acceleration could be equal to zero in which case the velocity would remain constant) in a straight line relative to a galilean coordinate system k, then it will also be at rest or moving with constant acceleration in a straight line relative to a second coordinate system k' provided the law of inertia is valid in system k' (in other words, provided it is a galilean coordinate system).