This is "vecdeque-stableix", a deque with stable index values.

Copyright (C) 2019-2020 Ian Jackson

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License v3 along with this program, in the file GPL-3.
If not, see <http://www.gnu.org/licenses/>.


Formalities
-----------

Individual files generally contain the following tag in the copyright
notice, instead of the full licence grant text:
  SPDX-License-Identifier: GPL-3.0-or-later
As is conventional, this should be read as a licence grant.

Contributions are accepted based on the git commit Signed-off-by
convention, by which the contributors' certify their contributions
according to the Developer Certificate of Origin version 1.1 - see
the file DEVELOPER-CERTIFICATE.

If you create a new file please be sure to add an appropriate licence
header, probably something like this:
// Copyright by contributors to the otter game system
// SPDX-License-Identifier: GPL-3.0-or-later
// There is NO WARRANTY.