BMcM> I haven't deleted the Z_prime entry, though you have indicated BMcM> that you will pull it from consideration at this stage (though I remark that BMcM> there have been requests from other sources for a record of Z', so finding a BMcM> sound definition would be a useful priority for the next version). I sort of agree. The above Z' is rather crude. What is really required, according to me, is a CIF encoding for the molecular symmetry (crystallographic and non-crystallographic) and chirality of all molecules in the asymmetric unit. It seems that this must be in a loop so that one knows which symmetry belongs to which type of molecule. It is too much to ask that this be implemented in the current revision. On the other hand many structures only have one type of molecule in them. In this case the suggested Z' would serve a purpose if the wording could be beefed up to make it clear that it only deals with the one-type-of-chemical-molecule case. Very many structures are like this and so the CIF item would be useful. I'm sure that the editors of Acta Cryst C and E could fairly easily be convinced that such information should become obligatory immediatetly in their journals. For the moment the more complicated cases could be dealt with by text in the body of the article or a CIF comment item. My counter example is that of a 'co-crystal' in which there are several different independent molecules. There was a poorly attended meeting at the IUCr Congress in Geneva which started to discuss nomenclature for co-crystals. The chair of the nomenclature commission was there. The prime mover is located at the CCDC. I wonder what is going on. BMcM> Nor have BMcM> I included either of Howard's alternative definitions for BMcM> _space_group_symop_operation_xyz I'm not surprised. The problem is to know which one is correct. I did not look but perhaps there is some small print in the symmetry cif dic which makes it clear. I do not have time myself to look. H.
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