Sentence:  In Chap. 4 the fundamental concepts on Lie <WSD>groups</WSD> have been introduced through the SO(3) <WSD>group</WSD> and its covering <WSD>group</WSD> SU(2). 
Meaning of the word marked with <WSD> tags:  A set with an associative binary operation, under which there exists an identity element, and such that each element has an inverse.