There is a cloud in the Yellow Emperor's canon: the spleen dominates the center, and it is often hidden for four days, 18 days each. Each delivery 18 days, what is the solution?

Four o'clock is the last eighteen days of the last month in each of the four seasons. It is the ugly, ugly, unfinished and embarrassing four months of the lunar calendar (these four months and five elements belong to the soil). Strictly speaking, the Qingming Festival of the lunar calendar, Grain Rain is the month; Small summer heat is not a month; Cold dew, the first frost is the month; Slight cold and severe cold are ugly months, and months are not divided by specific dates.