text: 1. Check to see if the Pellet reasoner is installed. Click on the Reasoner menu. At the bottom of the menu 
  there will be a list of the installed reasoners such as Hermit and possibly Pellet. If Pellet is visible in that 
  menu then select it and skip to step 3. 
  
  2. If Pellet is not visible then do File>Check for plugins and select Pellet from the list of available plugins 
  and then select Install. This will install Pellet and you should get a message that says it will take effect the 
  next time you start Protégé. Do a File>Save to save your work then quit Protégé and restart it. Then go to 
  File>Open recent. You should see your saved Pizza tutorial in the list of recent ontologies. Select it to 
  load it. Now you should see Pellet under the Reasoner menu and be able to select it so do so. 
  
  3. With Pellet selected in the Reasoner menu execute the command Reasoner>Start reasoner. The 
  reasoner should run very quickly since the ontology is so simple. You will notice that the little text 
  message in the lower right corner of the Protégé window has changed to now say Reasoner active. The 
  next time you make a change to the ontology that text will change to say: Reasoner state out of sync with 
  active ontology. With small ontologies the reasoner runs very quickly, and it is a good idea to get into the 
  habit of running it often, as much as after every change. 
  
  4. It is possible that one or more of your classes will still be highlighted in red after you run the reasoner. 
  If that happens do: Window>Refresh user interface and any red highlights should go away. Whenever 
  your user interface seems to show something you don’t expect the first thing to do is to try this command. 
  
  5. One last thing we want to do is to configure the reasoner. By default, the reasoner does not perform all 
  possible inferences because some inferences can take a long time for large and complex ontologies. In 
  this tutorial we will always be dealing with small and simple ontologies so we want to see everything the 
  reasoner can do. Go to: Reasoner>Configure. This will bring up a dialog with several check boxes of 
  inferences that the reasoner can perform. If they aren’t all checked then check them all. You may receive 
  a warning that some inferences can take a lot of time, but you can ignore those since your ontology will 
  be small. 
  
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  4.3 Disjoint Classes 
  
  Having added the classes Pizza, PizzaTopping, and PizzaBase to the ontology, we now want to say 
  that these classes are*disjoint*. I.e., no individual can be an instance of more than one of those classes. In 
  set theory terminology the intersection of these three classes is the empty set: owl:Nothing. 
  
  **Exercise 6: Make Pizza, PizzaTopping, and PizzaBase disjoint from each other**
  
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