That's because there aren't any. But, as I said earlier, the chord progression in the former is pretty much the same as Let's Get It On with one exception. The rhythmic movement of the backing music is similar too. Considering his live performances of the song often incorporating Let's Get It On, you've got a pretty strong case for a lawsuit.
Robin and Pharrell got done for stealing a vibe. That's a precedent, and a very dangerous one. But I can tell you why Robin and Pharrell lost the Blurred Lines case. From what I read about the case at the time, both came across as arrogrant in their testimonies. Not something that's going to endear you to a dury.
As a slight aside, Ed Sheeran has become a very derivative songwriter. Pretty easy to reference the songs he's nicking.
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