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Re: CIF description of twinning




Comments on the Twin items:
---------------------------
_diffrn_reflns_twin_id
The description should read: 'A unique identifier for each possible domain
state.'  The phrase 'whose presence is assumed to be permissible' is
complex and confusing.

_refine_ls_twin_fraction The sentence 'It is mandatory to specify...
domain states' should be replaced by 'The refined twin fractions of all
domain states should be given'.  The word mandatory is reserved for items
(such as _*_id) that are required for file management.  All other items,
according to CIF rules, are optional.  A rather more gentle reminder is
needed that nothing of significance should be omitted since there are no
default values.


			David


*****************************************************
Dr.I.David Brown,  Professor Emeritus
Brockhouse Institute for Materials Research, 
McMaster University, Hamilton, Ontario, Canada
Tel: 1-(905)-525-9140 ext 24710
Fax: 1-(905)-521-2773
idbrown@mcmaster.ca
*****************************************************



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