On a community-driven site like the Tricki, one has to be a bit careful about how one handles copyright issues. The most appropriate solution that we have found so far involves placing all the contributed content on the Tricki under a licence that gives other people the right to modify the content and contribute to it. We have initially decided to use a Creative Commons licence for this.
The Creative Commons licence on the Tricki
By uploading content to the Tricki, users agree to license the content under the Creative Commons Attribution Non-Commercial Share Alike licence, which gives other people certain rights to copy, modify and distribute the content. In order to be able to license your contributions in this way, you must make sure that the copyright holder of the content that you are adding (which will most likely be you if you have written the content yourself) expressly permits that the content should come under such a licence. If you wish to grant additional rights when creating or modifying an article, such as allowing for commercial use without your permission needing to be sought, you should specify this in the revision information box when submitting the data. Note that such rights will only be granted to the specific additions that you upload or the specific changes that you make and not to content uploaded by others in the same article.
In other words, if you write an article, others will be free to edit it and reproduce it for non-commercial purposes. You should therefore not copy any other material and include it in a Tricki article unless its copyright holder also accepts the above licence. And if you want to allow commercial use of your article, then you can specify this, but you should note that if others make non-minor additions to your article, then they are the ones with the right to decide about those additions.
An example that might actually occur is if you wish to write a textbook in which you use some Tricki material that you have written. You would have the right to do this, but if substantial changes have been made by other people then you should either use earlier versions written by you or should ask for their permission. Of course, nobody has a monopoly on a mathematical example, so if they do not give permission, you still have the option of expressing somebody else's insight in your own words.
The above licensing terms also apply to comments and forum posts (since these will quite often contain suggestions for additions or changes to articles), though for these types of content there is no revision log where you can automatically grant additional rights.
The licence gives anyone the right to copy, modify or distribute a contributed piece of content on the Tricki. There are, however, some conditions that are imposed upon such use. One condition is that one must include proper attribution: in the context of the Tricki, it should suffice to give the name(s) (or username(s)) of the person(s) whose work you are using as well as a URL to the original piece of content. Note also that any work that makes use of Tricki material in this way must again be licensed under the same terms.
Granting additional rights
The copyright holder of a piece of content can grant further rights than those guaranteed by the licence, such as allowing for commercial use. If you wish to grant additional rights, you should do so by adding a note to the revision log specifying what additional rights that you are granting. If you wish to allow for commercial use, we suggest adding the text "CUA" to the log, meaning "Commercial Use Allowed", in order to keep clutter in the logs down.
There is a discussion on the forums about licensing.