Short version for non-lawyers:
The rust-permutation is dual-licensed under Apache 2.0 and MIT
terms.
Longer version:
The Rust-Permutation library is copyright 2017, Jeremy Salwen
Licensed under the Apache License, Version 2.0
<LICENSE-APACHE or
http://www.apache.org/licenses/LICENSE-2.0> or the MIT
license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
at your option. All files in the project carrying such
notice may not be copied, modified, or distributed except
according to those terms.