The derivation given here and illustrated in Fig. 3-5 is based on one presented by Bais and makes use of previous results from the Relativistic Composition of Velocities, Time Dilation, and Length Contraction sections. Event P has coordinates (w, x) in the black "rest system" and coordinates (w ′, x ′) in the red frame that is moving with velocity parameter β = v / c. To determine w ′ and x ′ in terms of w and x (or the other way around) it is easier at first to derive the inverse Lorentz transformation.