## IGL copyleft subdirectory

Functions in the `include/igl/copyleft/` subdirectory are in the
`igl::copyleft::` namespace to indicate that they are under a more aggressive
[copyleft](https://en.wikipedia.org/wiki/Copyleft) than
[MPL2](https://en.wikipedia.org/wiki/Mozilla_Public_License) used for the main
`include/igl` directory and `igl::` namespace. Most notably, this subdirectory
includes code that is under
[GPL](https://en.wikipedia.org/wiki/GNU_General_Public_License).

Typically a company planning on developing software without releasing its
source code will avoid or purchase licenses for such dependencies. If you do
obtain such a license for the dependencies employed here, you are free to use
the libigl functions here as per their MPL2 license.
