https://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%3D+%7B%5Cbf+E%7D+%5Csum_%7B1+%5Cleq+i_1+%3C+%5Cldots+%3C+i_k+%5Cleq+n%7D+F%28%5Clambda_1%28M_n%29%2C%5Cldots%2C%5Clambda_k%28M_n%29%29.&bg=ffffff&fg=000000&s=0&c=20201002