Licence question...

[Sean Charles]

If I create an executable with "gplc" consisting of which is both pure Prolog 
and custom "C" interface code, under the terms of the GNU licence, am I at 
liberty to sell that executable as a commercial product ?

If not, why not and what would I have to do to remain within the rules ?

I have read and re-read the various GNU docs etc. but not being a legal eagle I 
am afraid it has all left me feeling rather dazed and confused as to what is 
and what is not permissible etc.

I certainly don't want to "fall foul" of such a wonderful community and should 
my "product" ever see the light of day I'd be deliriously happy to be able to 
one day be in a position to fund some proper developer time to boost the 
progress of GNU Prolog… indeed that would be awesome!

Thanks all,
Sean.