Sentence:  The invention of a derivative of a finite <WSD>partially ordered set</WSD> by Nazarova and Roiter in the late 1960s or early 1970s was a seminal event in the subject of representations of finite <WSD>partially ordered sets</WSD> (see [Simson 92]). 
Meaning of the word marked with <WSD> tags:  The ordered pair comprising a set and its partial order.