Hi there!

In the Esperanto Wikisource we have get a licensing problem. Can you help us, please?

In the Esperanto User Group we have successfully advocated at the World Esperanto Association to free their press communications, so we can put them into Esperanto Wikisource. I have putted the first one as a test [1] but was alerted about possible license incompatibility.

The material is under CC BY 4.0 but Wikisource is using CC BY-SA 3.0. (so the problem is the version number) The argument is, that CC licenses are "forward compatible" but not "retro compatible". So it is OK to put CC BY 3.0 material into CC BY 4.0 repository, but not the opposite. 

In the meantime I have found, that another Wikisources are collecting materials under CC BY 4.0, like https://en.wikisource.org/wiki/Category:CC_attribution_4.0

If it is OK to use CC BY 4.0 material in Wikisource, can you make some short legal reasoning so I can inform the Esperanto community? (and if it is not OK, we should think about the content already in use, like the linked one upper)

[1] https://eo.wikisource.org/wiki/Vikipedio_en_Esperanto_atingas_sian_250-milan_artikolon