code: @Override
      public void addSubPropertyOfAxiom(ObjectPropertyExpression ope1, ObjectPropertyExpression ope2) throws InconsistentOntologyException {
          checkSignature(ope1);
          checkSignature(ope2);
          objectPropertyAxioms.addInclusion(ope1, ope2);
      }
docs: Normalizes and adds an object subproperty axiom
  <p>
  SubObjectPropertyOf := 'SubObjectPropertyOf' '(' axiomAnnotations
  ObjectPropertyExpression ObjectPropertyExpression ')'
  <p>
  Implements rule [O1]:<br>
  - ignore the axiom if the first argument is owl:bottomObjectProperty
  or the second argument is owl:topObjectProperty<br>
  - replace by a disjointness axiom if the second argument is owl:bottomObjectProperty
  but the first one is not owl:topObjectProperty<br>
  - inconsistency if the first is  owl:topObjectProperty but the second is owl:bottomObjectProperty
  
  @throws InconsistentOntologyException