checkCIF procedure

PLAT914

 This ALERT reflects the notion that a dataset should contain a sufficient  
 number of Bijvoet (Friedel) pairs for the reliable determination of the
 absolute structure of a non-centrosymmetric crystal structure. 
 This test is invoked when a Flack parameter value is specified.
 Note: SHELXL97 will calculate/report a Flack parameter value even for  
 refinement against Friedel merged data. Remove the Flack entry from the CIF.