https://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cmathbf%7Br%7D_+1+%3A+%3D+C+%5Crightarrow+%5Clangle+f%2C+e_1%2C+%5Csim_1%2C+%5Cphi_+1+%5Crangle+%5C%5C+%5Cmathbf%7Br%7D_+2+%3A+%3D+C+%5Crightarrow+%5Clangle+f%2C+e_2%2C+%5Csim_2%2C+%5Cphi_+2+%5Crangle+&bg=ffffff&fg=333333&s=0&c=20201002