Dirac Spinor: 4 component object that transforms under boost and rotations according to a Ki, Ji matrices.

The most important finite dimensional almost irreducible rep of L+ is the 
dirac spinor.  
if {Gu,Gn}=anticommutator=-2nuv (a dirac algebra) => Sun=i/4[Gu,Gn].

Gu's are 4x4 matrices.
G0=
	O I2
	I2 0

Gi=
	0  Si
	-Si 0

Ki=S0i=i/4*[G0,Gi]= -i/2*
	
	Si 0
	0 -Si
	
Ji= .5*eijk Sjk= .5*

	Si 0
	0 Si