text: 4.10.4 Detecting a Class that can’t Have Members 
  Next, we are going to use the reasoner to detect a class with a definition that means it can never have any 
  members. In the current version of Protégé when the reasoner detects an inconsistency or problem on 
  some operating systems the UI can occasionally lock up and be hard to use. So to make sure you don’t 
  lose any of your work save your ontology using File>Save. 
  
  Sometimes it can be useful to create a class that we think should be impossible to instantiate to make sure 
  the ontology is modeled as we think it is. Such a class is called a Probe Class. 
  
  **Exercise 19: Add a Probe Class called ProbeInconsistentTopping**
  
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