t ′ = γ γ ( t − − v x / c 2 ) , x ′ = γ γ ( x − − v t ) etc., most often really mean Δ Δ t ′ = γ γ ( Δ Δ t − − v Δ Δ x / c 2 ) , Δ Δ x ′ = γ γ ( Δ Δ x − − v Δ Δ t ) etc. Although for brevity the Lorentz transformation equations are written without deltas, x means Δ x, etc. We are, in general, always concerned with the space and time differences between events.