Writing the Minkowski metric as a block matrix, and the Lorentz transformation in the most general form, η η = [ − − 1 0 0 I ] , Λ Λ = [ Γ Γ − − a T − − b M ] , carrying out the block matrix multiplications obtains general conditions on Γ, a, b, M to ensure relativistic invariance. Not much information can be directly extracted from all the conditions, however one of the results Γ Γ 2 = 1 + b T b is useful; b b ≥ 0 always so it follows that Γ Γ 2 ≥ ≥ 1 ⇒ ⇒ Γ Γ ≤ ≤ − − 1 , Γ Γ ≥ ≥ 1