Copyrights in the "group" library are retained by their contributors. No
copyright assignment is required to contribute to the "group" library.

The "group" library is licensed under either of

 * Apache License, Version 2.0, (see ./LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
 * MIT license (see ./LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally
submitted for inclusion in the work by you, as defined in the Apache-2.0
license, shall be dual licensed as above, without any additional terms or
conditions.