Book recommendation for self study of General relativity I am a second year Chemical Engineering student. However out of interest I wish to learn General theory of relativity. Can anyone please suggest some books for learning this subject?
Books for general relativity What are some good books for learning general relativity?
Why can partial derivatives be exchanged? In the   post in this stack exchange, one of the answers to the questions of do partial derivatives commute is: Second order partial derivatives commute if f is $C^2$ (i.e. all the second partial derivatives exist and are continuous). This is sometimes called Schwarz's Theorem or Clairaut's Theorem. This theorem is in my textbooks, yet I cannot seem to find the proof in them. I have tried proving the theorem yet I have gotten stuck. So, what is the proof of Clairaut's Theorem, or why do partial derivatives commute? If the proof is too long, a link to the proof with an intuitive explanation will be sufficient.