The application of direct methods to centrosymmetric structures containing heavy atoms. III

Direct methods are applied to difference-structure factors for a structure containing one or more heavy atoms at known special or pseudo-special positions, such that the heavy atoms do not contribute to several reflection parity groups. Phases of reflections in these parity groups, represented by symbols, are analysed by the sign-correction method. Phases as well as amplitudes of the difference-structure factors are refined by the general DIRDIF procedure as described previously.