Exercises: GNU, copyleft and licenses

Explain in your own words the relationship between the GNU project (started in 1983 by Richard Stallman to create a free operating system) and the Linux kernel (written by Linus Torvalds in 1991), and why the complete system is usually called GNU/Linux. Also define what copyleft is using the analogy of a shared recipe that forces you to share its variations.

A company takes a copyleft-licensed program, improves it and sells the improved version without publishing the code of its improvements. Explain whether it respects the license and why, what the program's community can do about it, and what would have changed if the original license had been a permissive one (for example, MIT or BSD), which does allow derivative works to be closed.