There is a detailed proof in
Lee, J. M., _Introduction to smooth manifolds_ , Second Edition, Springer (2013).
The result you are looking for is Theorem 21.18 on page 552.
There is a detailed proof in
Lee, J. M., _Introduction to smooth manifolds_ , Second Edition, Springer (2013).
The result you are looking for is Theorem 21.18 on page 552.