Expanding the exponentials in their Taylor series obtains B ( ζ ζ ) = I − − sinh ⁡ ⁡ ζ ζ ( n ⋅ ⋅ K ) + ( cosh ⁡ ⁡ ζ ζ − − 1 ) ( n ⋅ ⋅ K ) 2 R ( θ θ ) = I + sin ⁡ ⁡ θ θ ( e ⋅ ⋅ J ) + ( 1 − − cos ⁡ ⁡ θ θ ) ( e ⋅ ⋅ J ) 2 . which compactly reproduce the boost and rotation matrices as given in the previous section.