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(Ballet) I agree that the extensions are more important than the primary, and that the best solution is to have them the general keywords in both the extensions and the primary.
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(Ballet) I don't think it is a good idea to change the names. The INSTRUME and TELESCOP keywords are there to indicate which intruments we are dealing with. Better keep standard names for the EVENTS and GTI extensions, as was done for previous missions such as Chandra or XMM-Newton. I agree to the EXTVERS suggestion.
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