Note that function P -1 RP(x) combined operator transforms the point x in fractional space expressed using the P1121/a basis by first transforming its coordinates to the P21/c basis (P), carrying out the operation R (x,y+1/2,-z+1/2) in that setting, and then transforming the resulting point back to the P1121/a basis (P -1 ). The various parts of this calculation are shown in Table .