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

[Hubert Figuiere]

On Tue, 2008-11-04 at 13:02 +0100, thomas wrote:
> 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:
> -------------
> 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?
> -------------
> 
> The Answer was:
> 
> -------------
> No, Profili is not a GPL application, as it uses XFoil executable and
> not XFoil source code. 
> -------------

The question is how does this program use xfoil? By calling the
executable or by linking the xfoil code into it?

If it just call the executable it is fine. If it links the xfoil code,
either statically or dynamically, then it is a derivative of xfoil, and
therefor subject to the GPL licensing terms.

Hub