text: A closure axiom on a property consists of a universal restriction that says that a property can only be 
  filled by specified fillers. The restriction has a filler that is the union of the fillers that occur in the 
  existential restrictions for the property. For example, the closure axiom on the hasTopping property for 
  MargheritaPizza is a universal restriction that acts along the hasTopping property, with a filler that 
  is the union of MozzarellaTopping and also TomatoTopping. i.e. hasTopping only 
  (MozzarellaTopping or TomatoTopping). 
  
  **Exercise 23: Add a Closure Axiom on the hasTopping Property for MargheritaPizza**
  
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  1. Make sure that MargheritaPizza is selected in the class hierarchy in the Classes tab. 
  
  2. Click on the Add icon (+) next to the SubClass Of field in the Description view. 
  
  3. Select the Class expression editor tab from the pop-up window. Type in the Description Logic axiom: 
  hasTopping only (MozzarellaTopping or TomatoTopping). 
  
  4. Click on OK. 
  
  5. Repeat steps 1-4 but this time click on SohoPizza and use the axiom: hasTopping only 
  (MozzarellaTopping or TomatoTopping or ParmesanTopping or OliveTopping). 
  
  6. Synchronize the reasoner. 