https://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cint_0%5Et%5Cvert%5Cxi%5Cvert%5C%2C%5Cvert+d%5BX%2CY%5D%5Cvert%5Cle%5Csqrt%7B%5Cint_0%5Et%5Cxi%5E2%5C%2Cd%5BX%5D_t%5C%2C+%5BY%5D_t%7D%3C%5Cinfty.+&bg=ffffff&fg=000000&s=0&c=20201002