Four Books & Five Classics：四書五經 Four Books：四書 Great Learning (大學) 、Doctrine of the Mean (中庸)、 Analects of Confucius (論語)、Mencius (孟子)。 Five Classics：五經 Classic of Changes (易經)、Classic of Poetry (詩經)、 Classic of Rites (禮記)、Classic of History (書經)、Spring and Autumn Annals (春秋)。

“Classic of Changes” or “Book of Changes”, is one of the oldest of the Chinese classic texts, is a symbol system used to identify order in chance events. The text describes an ancient system of cosmology and philosophy that is intrinsic to ancient Chinese cultural beliefs. The cosmology centres on the ideas of the dynamic balance of opposites, the evolution of events as a process, and acceptance of the inevitability of change. In Western cultures and modern East Asia, “Book of Changes” is sometimes regarded as a system of divination. The classic consists of a series of symbols, rules for manipulating these symbols, poems, and commentary.

"Three rules must be obeyed and the four feminine virtuesthe"(三从四德)is one of the traditional chinese cultural opions in the 5 classics and 4 books. Not only women ,but men are required to obeyed this rule.so it makes chinese people lack of independence.Evrey thing or assignment to himself is aranged by others

Do you want know something about Confucianism.5 CLASSICS《诗经》、《尚书》、《礼记》、《周易》和《春秋》 4 BOOKS《论语》、《孟子》、《大学》和《中庸》

BTW, the most difficult book is, of course, "Classic of Changes (易經)".