1. The problem statement, all variables and given/known data The problem puts forth and identity for me to prove: or . It says that I can use "straight-forward" calculation to solve this using the definition of nabla or I can use Gauss's and Stoke's Theorum on an example in which I have a solid 3D shape nearly cut in two by a curve C. 2. Relevant equations Divergence Theorum Stoke's Theorum 3. The attempt at a solution I just can't seem to figure out how to start this. The two equations above are clearly suited to proving this identity, but I just can't see how.