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Summary

The graph was created by Robert Vienneau and is used with his permission. He explicitly gives the permission in the comments of his blog here: https://www.blogger.com/comment.g?blogID=26706564&postID=8884880137111486330

Licensing

I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.