GPL, BSD, commercial

[Michele Bosi]

Hello everyone,

I developed an opensource program A which uses a library B distributed
with 3 licenses, GPL3, LGPLv2.1 and a "commercial" one for
closed-source development. For the development a file F of my program
A I used the GPL3 version of library B. I was wondering if I can
distribute (and maybe even sell) the sources of my program A
(including F) using just any license like for example the BSD or if I
*have to* distribute F separately with the GPL3 license sice I used
the GPL3 version of the library B to develop it. The second question
is: if for example I sell my program A (including F) to a customer
with a commercial license written by me, will he/she be able to
develop closed-source produtcs? My answer to this last question is
"yes" as long as my customer has also a "commercial license" of
library B and as long as the sources of my file F are available for
the others under the GPL3 (to fulfill the GPL3 requirements induced by
the use of library B)... but of course I would like to know your
opinion :)

Another way to reformulate this last question might be: if I develop a
program which uses a GPL3 library and I release the source code of my
program under the GPL3 license, can I also release/sell closed-source
commercial licenses for the same program to the customers that request
for it in order to develop closed-source programs?

Sorry for the intricacy of my questions :)

Thanks,

Michele