text: relations, transitive relations, and many more. An understanding of the basic concepts of set theory will 
  help the user get the most out of OWL but is not required. One of the benefits of Protégé is that it presents 
  an intuitive GUI that enables domain experts to define models without a background in set theory. 
  However, developers are encouraged to refresh their knowledge on logic and set theory. A good source is 
  the first 3 chapters in Elements of the Theory of Computation by Lewis and Papadamitrious. Another 
  good source is the PDF document*Overview of Set Theory*available at: 
  https://www.michaeldebellis.com/post/owl-theoretical-basics 
  
  3.1.1 Individuals 
  Individuals represent objects in the domain of interest. An important difference between OWL and most 
  programming and knowledge representation languages is that OWL does not use the Unique Name 
  Assumption (UNA). This means that two different names could actually refer to the same individual. For 
  example, “Queen Elizabeth”, “The Queen” and “Elizabeth Windsor” might all refer to the same 
  individual. In OWL, it must be explicitly stated that individuals are the same as each other, or different 
  from each other. Figure 3.1 shows a representation of some individuals in a domain of people, nations, 
  and relations — in this tutorial we represent individuals as diamonds. 