Below I have posted an excerpt of Lee's Book "Introduction to Smooth Manifolds" (page 371). I don't know what the symbol means that looks like a lower-right corner, and I cannot find it via the index, nor does any alternative source for the definition of the divergence operator have that symbol. If anybody could give a hint what it denotes I can maybe find the passage in the book where it is explained, that would be a HUGE help!!!


