https://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%7B%5Cmathcal+H%7D_%7B%5Cmu_2%7D%5Bv_i%5D+%3D+%5Cint_%7B%5Cpartial+%5COmega_i+%5Ccap+%5Cpartial+%5COmega%7D+u+%5Cpartial_n+u.&bg=ffffff&fg=000000&s=0