>223

 { [1,1,0] + [1,0,1] - [0,1,1] } /2 = [1,0,0],
 { [1,1,0] - [1,0,1] + [0,1,1] } /2 = [0,1,0],
 {-[1,1,0] + [1,0,1] + [0,1,1] } /2 = [0,0,1]
がR^3の基底ならば、そうだが。