Four Essential Classics is a big classical series of books published by China Publishing House.

Starting with"four should" to innovate party construction;

The name of "si bu" is originated in the early Jin period.

Wan Quan in Ming dynasty put forward to the following theory of health preserving in his Four Essentials for Health Preserving: being moderate in diet and sexual life to reinforce the spleen and kidney;being appropriate in movement and regulating the emotions;conforming to seasonal changes to nourish Zangfu organs and the physique;preventing and treating diseases actively and effectively.

The four-element method which can be applied in the design of large complex engineering systems is introduced in detail from basic concept,important characters and method of application.

The formula of four factors is given in analyzing first-order circuits,the initial value is extend as far as 0_ value and it is unanimously agreed other theory of circuit a- nalysis.