M. A. Cornea-Hasegan, Z. Zhang, R. E. Lynch, D. C. Marinescu, A. Hadfield, J. K. Muckelbauer, S. Munshi, L. Tong, and M. G. Rossmann. Phase Refinement and Extension by Means of Non-Crystallographic Symmetry Averaging Using Parallel Computers. Acta Crystallographica, D51:749-759, 1995.