The text of the Apertis website is copyrighted (automatically, under the Berne Convention) by Apertis editors and contributors and is formally licensed under Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA) unless explicitly stated otherwise.

The licenses that the Apertis website uses grant free access to our content in the same sense that free software is licensed freely. Apertis website content can be copied, modified, and redistributed if and only if the copied version is made available on the same terms to others and acknowledgment of the authors of the Apertis website article used is included (a link back to the article is generally thought to satisfy the attribution requirement; see below for more details). Copied Apertis website content will therefore remain free under appropriate license and can continue to be used by anyone subject to certain restrictions, most of which aim to ensure that freedom. This principle is known as copyleft in contrast to typical copyright licenses.

The English text of the CC BY-SA license is the only legally binding restriction between authors and users of the Apertis website content.

Contributors’ rights and obligations

If you contribute text directly to the Apertis website, you thereby license it to the public for reuse under CC BY-SA. Non-text media may be contributed under a variety of different licenses that support the general goal of allowing unrestricted re-use and re-distribution.

If you want to import text that you have found elsewhere or that you have co-authored with others, you can only do so if it is available under terms that are compatible with the CC BY-SA license.

You retain copyright to materials you contribute to the Apertis website, text and media. Copyright is never transferred to Apertis. You can later republish and relicense them in any way you like. However, you can never retract or alter the license for copies of materials that you place here; these copies will remain so licensed until they enter the public domain when your copyright expires (currently some decades after an author’s death).

Guidelines for images and other media files

Images, photographs, video and sound files, like written works, are subject to copyright. Images, video and sound files on the internet need to be licensed directly from the copyright holder or someone able to license on their behalf.

Re-use of text

  • Attribution: To re-distribute text from the Apertis website in any form, provide credit to the authors either by including a) a hyperlink (where possible) or URL to the page or pages you are re-using, b) a hyperlink (where possible) or URL to an alternative, stable online copy which is freely accessible, which conforms with the license, and which provides credit to the authors in a manner equivalent to the credit given on this website, or c) a list of all authors. (Any list of authors may be filtered to exclude very small or irrelevant contributions.) Copyleft/Share Alike: If you make modifications or additions to the page you re-use, you must license them under the Creative Commons Attribution-Share-Alike License 4.0 or later. Indicate changes: If you make modifications or additions, you must indicate in a reasonable fashion that the original work has been modified. If you are re-using the page in a website, for example, indicating this in the page history is sufficient. Licensing notice: Each copy or modified version that you distribute must include a licensing notice stating that the work is released under CC BY-SA and either a) a hyperlink or URL to the text of the license or b) a copy of the license. For this purpose, a suitable URL is:

For further information, please refer to the legal code of the CC BY-SA License.


This page applies only to the Apertis website. The Apertis code is licensed separately and the licenses can be found in the code repositories, normally in a file called COPYING.


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