represent, as a whole, an original work of authorship. For the purposes
      of this License, Derivative Works shall not include works that remain
      separable from, or merely link (or bind by name) to the interfaces of,
      the Work and Derivative Works thereof.

      "Contribution" shall mean any work of authorship, including
      the original version of the Work and any modifications or additions

pkg container/list, type List struct
pkg container/ring, func New(int) *Ring
pkg container/ring, method (*Ring) Do(func(interface{}))
pkg container/ring, method (*Ring) Len() int
pkg container/ring, method (*Ring) Link(*Ring) *Ring
pkg container/ring, method (*Ring) Move(int) *Ring
pkg container/ring, method (*Ring) Next() *Ring
pkg container/ring, method (*Ring) Prev() *Ring
pkg container/ring, method (*Ring) Unlink(int) *Ring