P 21 21 21,NR.19*GC,BE*
LATT -1
SYMM .5-X,  -Y,.5+Z
SYMM .5+X,.5-Y,  -Z
SYMM   -X,.5+Y,.5-Z
    0 .5 / 0 .5 / 0 1
    P 21 21 21,NR.19*GC,BE*