Let $A,B \in \mathbb{C}^{n\times n}$ be two normal matrices.
Is it true that:
$\sigma_{i}(AB) = \sigma_{i}(BA) \; \; \forall \; i$ where $\sigma_{i}$ is the $i$-th singular value of the corresponding matrix.
Any hint/comment/expalantion for proving this statement is appreciated.
Hints.