Considering a scenario where someone may wish to use avendish and release their source under a permissive license, or (aghast!) keep it closed source, I noticed that e.g. avnd/concepts/parameter.hpp with public domain licensing includes avnd/wrappers/widgets.hpp with a strong copy-left license; I realize that I am not sure then how to interpret the copyright status of the former. Doesn't including GPL code in your code mean you are obliged to release your code under the same license? Doesn't that mean that avnd/concepts/parameter.hpp, and anything else that includes avnd/wrappers/widgets.hpp or other GPL headers, is obliged to be licensed under the GPL? Is this a bug in avendish, or my understanding of the GPL?