In the book by Aapo Hyvärinen, it is shown that:
Where z is the white vector of a data matrix x, s are the IC's and à is the mixing matrix of the whitened data matrix z. My question is: If the matrix à is orthonormal as show above, does it implies that s is orthogonal as $\\E(ss^T)$ has to be $\\I$? If so should the IC's in this case be orthogonal?