There has been much debate over whether or not merely linking to a piece of code makes it a derivative work. I know FSF says "yes", so according to them I can't dynamically link a non-GPL compatible program to a GPL library and distribute the whole. But I could do that for private use, as long as no code is released to the public.

That made me wonder: what if I don't redistribute the GPL code at all? If my program can work alone (reinforcing my claim that it's not a derivative work), but can do more if the GPL library is also installed to the system, couldn't I just release my application under my own licensing terms - without including any GPL code - and post instructions for anyone interested to separately download the GPL code and do the integration "for their private use"?

I know it's against the "spirit" of the GPL, so I'm not suggesting it's a good idea to do that. However, this question is bugging me for some time, specially because of the implications of each answer:

If I can not do that:

• can I write another library with a similar API? (before answering "of course you can", remember that having the same API would allow both libraries to be swapped at will by my customers - so I don't need to work too hard on my library or even make it "working". How to determine if a similar program is just similar or is a circumvention attempt?)

If I can do that:

• can I also be paid to perform the service of installing the GPL library for a customer? (I sell them my program, install it in their machines, download and install the GPL library too)
• can I put the two programs in the same website? In two different CDs? (I know I said the idea was not to redistribute the GPL code, I'm just thinking in excuses people could use to claim they're not redistributing even though they are)