μ: miu, which is similar to [Mi You] in Chinese, can be replaced by the Latin letter M.

∑: σ, Chinese approximation [Sima] This should be the initial letter of the Greek word "sum", σ is its lowercase, and it can be directly replaced by the Latin letter S.

ρ: rho, which is similar to Chinese meat, can be replaced by the Latin letter R.

The numbers above and below ∑ are the range of summation of variables. ∑ (Xi- 1), with the number 5 above and I = 1 below, is the sum of (Xi-1) functions of this variable xi from X 1 to X5.