Let αT and αZ, respectively, be the angles of X and C for T and Z, respectively. Prove that sin(αZ/2)=sin(αT/2)β1ev In this case the factor of contraction also depends on the direction of X!
Again, we have X,T=C,T=1 and X,Z=β(1ev), C,Z=β; by (???) we thus obtain the result.