[phenixbb] Dual conformation on symmetry axis

[Pavel Afonine]

Hi,

> density on symmetry elements usually displays artefacts and is difficult to
> interpret.

I've seen this rumor perpetuated so many times.. I think I can also say 
"Fourier maps show artifacts anywhere in the unit cell volume (including 
symmetry elements) that originate, for example, from: a) finite 
resolution and partial completeness of the data, b) errors in crystal 
structure model (model is always used as a source of phase information), 
c) measurement errors. These artifacts are difficult (and unnecessarily) 
to interpret in terms of atomic model.". Are symmetry elements somewhat 
special in this regard (that is one sees more artifacts on symmetry 
elements than anywhere else)? If this is the case, can someone provide 
convincing reasoning for this (not hand-waving!)?

Thanks,
Pavel