Encyclopedia of Mathematics:License Notice

Any new text contributed to the Encyclopedia of Mathematics is copyrighted (automatically, under the Berne Convention) by Encyclopedia of Mathematics editors and contributors and is formally licensed to the public under one or several liberal licenses. Unless otherwise indicated, newly contributed texts are co-licensed under the Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA) and the GNU Free Documentation License (GFDL) (unversioned, with no invariant sections, front-cover texts, or back-cover texts).

The licenses the Encyclopedia of Mathematics uses grant free access to our content in the same sense that free software is licensed freely. Encyclopedia of Mathematics 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 Encyclopedia of Mathematics article used is included (a link back to the article is generally thought to satisfy the attribution requirement; see below for more details). Copied Encyclopedia of Mathematics 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.

To this end,

• Permission is granted to copy, distribute and/or modify the Encyclopedia of Mathematics' text under the terms of the Creative Commons Attribution-ShareAlike 3.0 Unported License and, the GNU Free Documentation License. unversioned, with no invariant sections, front-cover texts, or back-cover texts.
• A copy of the Creative Commons Attribution-ShareAlike 3.0 Unported License is included in the section entitled "Text of Creative Commons Attribution-ShareAlike 3.0 Unported License"
• A copy of the GNU Free Documentation License is included in the section entitled "GNU Free Documentation License".
• Content on the Encyclopedia of Mathematics is covered by disclaimers.

The English text of the CC-BY-SA and GFDL licenses is the only legally binding restriction between authors and users of Encyclopedia of Mathematics content. What follows is a common interpretation of CC-BY-SA and GFDL, as it pertains to the rights and obligations of users and contributors.

Contributors' rights and obligations

If you contribute text directly to the Encyclopedia of Mathematics, you thereby license it to the public for reuse under CC-BY-SA and GFDL (unversioned, with no invariant sections, front-cover texts, or back-cover texts). 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. See Guidelines for images and other media files, below.

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 do not need to ensure or guarantee that the imported text is available under the GNU Free Documentation License, unless you are its sole author. Furthermore, please note that you cannot import information which is available only under the GFDL. In other words, you may only import text that is (a) single-licensed under terms compatible with the CC-BY-SA license or (b) dual-licensed with the GFDL and another license with terms compatible with the CC-BY-SA license. If you are the sole author of the material, you must license it under both CC-BY-SA and GFDL.

If the material, text or media, has been previously published and you wish to donate it to the Encyclopedia of Mathematics under appropriate license, you will need to verify copyright permission through one of our established procedures. If you are not a copyright holder, you will still need to verify copyright permission; see the Using copyrighted work from others section below.

You retain copyright to materials you contribute to the Encyclopedia of Mathematics, text and media. Copyright is never transferred to Springer or to the European Mathematical Society. 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).

Using copyrighted work from others

All creative works are copyrighted, by international agreement, unless either they fall into the public domain or their copyright is explicitly disclaimed. Generally, the Encyclopedia of Mathematics must have permission to use copyrighted works. There are some circumstances under which copyrighted works may be legally utilized without permission; see Non-free content for specific details on when and how to utilize such material. However, it is our goal to be able to freely redistribute as much of the Encyclopedia of Mathematics' material as possible, so original images and sound files licensed under CC-BY-SA and GFDL (unversioned, with no invariant sections, front-cover texts, or back-cover texts) or in the public domain are greatly preferred to copyrighted media files used under fair use or otherwise.

If you want to import media (including text) that you have found elsewhere, you can only do so if it is public domain or available under terms that are compatible with the CC-BY-SA license. If you import media under a compatible license which requires attribution, you must, in a reasonable fashion, credit the author(s). You must also in most cases verify that the material is compatibly licensed or public domain. If the original source of publication contains a copyright disclaimer or other indication that the material is free for use, a link to it on the media description page or the article's talk page may satisfy this requirement. If you obtain special permission to use a copyrighted work from the copyright holder under compatible terms, you must make a note of that fact (along with the relevant names and dates) and verify this through one of several processes. See Requesting copyright permission for the procedure for asking a copyright holder to grant a usable license for their work and for the processes for verifying that license has been granted.

Never use materials that infringe the copyrights of others. This could create legal liabilities and seriously hurt the Encyclopedia of Mathematics. If in doubt, write the content yourself, thereby creating a new copyrighted work which can be included in the Encyclopedia of Mathematics without trouble.

Note that copyright law governs the creative expression of ideas, not the ideas or information themselves. Therefore, it is legal to read an encyclopedia article or other work, reformulate the concepts in your own words, and submit it to the Encyclopedia of Mathematics, so long as you do not follow the source too closely. (Please refer to this Copyright FAQ for more on how much reformulation may be necessary as well as the distinction between summary and abridgment.) However, it would still be unethical (but not illegal) to do so without citing the original as a reference.

Linking to copyrighted works

Since most recently-created works are copyrighted, almost any Encyclopedia of Mathematics article which cites its sources will link to copyrighted material. It is not necessary to obtain the permission of a copyright holder before linking to copyrighted material, just as an author of a book does not need permission to cite someone else's work in their bibliography. Likewise, the Encyclopedia of Mathematics is not restricted to linking only to CC-BY-SA or open-source content.

However, if you know or reasonably suspect that an external Web site is carrying a work in violation of the creator's copyright, do not link to that copy of the work. An example would be linking to a site hosting the lyrics of many popular songs without permission from their copyright holders. Knowingly and intentionally directing others to a site that violates copyright has been considered a form of contributory infringement in the United States (Intellectual Reserve v. Utah Lighthouse Ministry [1]). Linking to a page that illegally distributes someone else's work sheds a bad light on the Encyclopedia of Mathematics and its editors.

Context is also important; it may be acceptable to link to a reputable website's review of a particular film, even if it presents a still from the film (such uses are generally either explicitly permitted by distributors or allowed under fair use). However, linking directly to the still of the film removes the context and the site's justification for permitted use or fair use.

Copyright violations

Contributors who repeatedly post copyrighted material despite appropriate warnings may be blocked from editing by any administrator to prevent further problems.

If you suspect a copyright violation, you should at least bring up the issue on that page's discussion page. Others can then examine the situation and take action if needed. Some cases will be false alarms. For example, text that can be found elsewhere on the Web that was in fact copied from the Encyclopedia of Mathematics in the first place is not a copyright violation on Encyclopedia of Mathematics's part.

If a page contains material which infringes copyright, that material – and the whole page, if there is no other material present – should be removed. See Copyright violations for more information, and Copyright problems for detailed instructions.

Guidelines for images and other media files

Images, photographs, video and sound files, like written works, are subject to copyright. Someone holds the copyright unless they have been explicitly placed in the public domain. 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. In some cases, fair use guidelines may allow them to be used irrespective of any copyright claims; see Non-free content for more.

Image description pages must be tagged with a special tag to indicate the legal status of the images, as described at Image copyright tags. Untagged or incorrectly-tagged images will be deleted.

Works by the United States Federal Government

Works produced by civilian and military employees of the United States federal government in the scope of their employment are public domain by statute in the United States (though they may be protected by copyright outside the U.S.). It is not enough that the employee was working at the time; he/she must have made the work as part of his/her duties (e.g. a soldier who takes a photograph with his/her personal camera while on patrol in Iraq owns the copyright to the photo, but it may find its way onto a unit webpage or otherwise be licensed to the government).

However, not every work republished by the U.S. government falls into this category. The U.S. government can own copyrights that are assigned to it by others – for example, works created by contractors.

Moreover, images and other media found on .mil and .gov websites may be using commercial stock photography owned by others. It may be useful to check the privacy and security notice of the website, but only with an email to the webmaster can you be confident that an image is in the public domain.

See Public domain for further information. But note that while the United States government does not claim copyright protection on its own works, governments outside the U.S. often do claim copyright over works produced by their employees (for example, Crown copyright in the United Kingdom).

Works by state governments of the United States

In addition, most state and local governments in the United States do not release their work into the public domain and do in fact own the copyright to their work. Please make sure to check copyright information before using their work.

Re-use of text

Attribution

To re-distribute text on the Encyclopedia of Mathematics 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.) This applies to text developed by the Encyclopedia of Mathematics community. Text from external sources may attach additional attribution requirements to the work, which should be indicated on an article's face or on its talk page. For example, a page may have a banner or other notation indicating that some or all of its content was originally published somewhere else. Where such notations are visible in the page itself, they should generally be preserved by re-users.

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 3.0 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 wiki, 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: http://creativecommons.org/licenses/by-sa/3.0/

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

Additional availability of text under the GNU Free Documentation License

For compatibility reasons, any page which does not incorporate text that is exclusively available under CC-BY-SA or a CC-BY-SA-compatible license is also available under the terms of the GNU Free Documentation License. In order to determine whether a page is available under the GFDL, review the page footer, page history, and discussion page for attribution of single-licensed content that is not GFDL-compatible. All text published before June 15th, 2009 on the Encyclopedia of Mathematics was released under the GFDL, and you may also use the page history to retrieve content published before that date to ensure GFDL compatibility.