This widget is a button to launch a select file window 
to choose the name of an already existing prefix file
or verify that the name has not already been taken in 
a previous calculation.
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 SYRTHES version   : VERSION_SYRTHES
 Name help file  : Fn_Rnp_but.html
 I. Rupp, C. Peniguel  -  may 2014
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