Fuente TeX:

(x,y,z,t)= x(1,0,0,0) + y (0,1,0,0)+ \frac{(z-t)}{2}(0,0,1,-1)+ \frac{(z+t)}{2}(0,0,1,1)\\ (2,-1,0,0)= 2(1,0,0,0) -1(0,1,0,0)\\ (0,0,4,-2)=3 (0,0,1,-1) + 1 (0,0,1,1)