群-一种“公理化”定义的代数系统 The law of composition is associative.That is, 问题2：结合律 (aob)oc=ao(boc) 为什么会被放进 fora,b,c∈G. 群公理中？ There exists an element e G,called the identity element,such that for any element a EG eo a aoe a. For each element a G,there exists an inverse element in G, denoted by a-1,such that aoa-1=a-loa=e.群 – 一种“公理化”定义的代数系统 问题2：结合律 为什么会被放进 群公理中？