New candidate JEP: 431: Sequenced Collections

[Mark Reinhold]

https://openjdk.org/jeps/431

  Summary: Introduce new interfaces to represent collections with a
  defined encounter order. Each such collection has a well-defined first
  element, second element, and so forth, up to the last element. It also
  provides uniform APIs for accessing its first and last elements, and
  for processing its elements in reverse order.

- Mark