{VPB[4, xp[1, 2]], VPB[4, xm[1, 2]], VPB[4, xp[1, 3]], VPB[4, xm[1, 3]], 
 VPB[4, xp[1, 4]], VPB[4, xm[1, 4]], VPB[4, xp[2, 1]], VPB[4, xm[2, 1]], 
 VPB[4, xp[2, 3]], VPB[4, xm[2, 3]], VPB[4, xp[2, 4]], VPB[4, xm[2, 4]], 
 VPB[4, xp[3, 1]], VPB[4, xm[3, 1]], VPB[4, xp[3, 2]], VPB[4, xm[3, 2]], 
 VPB[4, xp[3, 4]], VPB[4, xm[3, 4]], VPB[4, xp[4, 1]], VPB[4, xm[4, 1]], 
 VPB[4, xp[4, 2]], VPB[4, xm[4, 2]], VPB[4, xp[4, 3]], VPB[4, xm[4, 3]]}
