A Program use xfoil (GPL) but is not GPL. Is this possible?

[thomas]

Hi,
        
I found the Program Profili2 (don't know the license, but not GPL
compatible). This program uses XFoil (GPL, see
http://web.mit.edu/drela/Public/web/xfoil/ ). Must Profili use GPL, too?
There is no sourcecode for Profili available. 

I wrote a E-Mail to the Author of Profili:
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i saw that profili2 use XFoil for calculations. XFoil use the GPL as
license. My question is, where can i download the sourcecode from
Profili? I think Profili should use also the GPL because you use XFoil.
Is that right or not?
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The Answer was:

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No, Profili is not a GPL application, as it uses XFoil executable and
not XFoil source code. 
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Best regards,
        
Tom