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I'll use Qt as an exmaple:

If I use Qt for a commercial software, I have to consider the Qt licensing, but at the same time Qt states many own third party components with different FOSS licenses. e.g.

Each of those third-party dependencies may have its own dependencies with different licenses. And each of those dependencies may have...

Now if I want to release an application (commercial license) which uses Qt under LGPL (as shared library), is it sufficient to comply with LGPL for the "first level" (Qt), i.e.

  • provide the LGPL and GPL license
  • state the third party component used
  • describe a way to exchange the Qt shared lib
  • if my GUI shows copyright notices, also show Qt's copyright/license

?

Or will I have "recursively" to dig into Qt's third party components, provide the license and maybe source code for each of those?

Of course this question is not limited to Qt, but to third party components in general which make use of other third party components

  • Yes, in general you must fulfill all license obligations. But the Qt project uses only 'compatible' third party code. For example, none of the third-party projects on the page you mentioned would require you to supply separate source code. Complying is done in the way Qt have shown (by providing a documentation page for it). However, suppose you added a third party library to make an 'enhanced' Qt and suppose that extra third party library had a GPL license. Now, anyone using your enhanced Qt would have to comply with that project's license as well (GPL), even if 'enhanced Qt' is still LGPL. – Brandin Mar 6 '18 at 15:28

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