code: protected PExp makeOr(PExp root, PExp e)
  	{
  		if (root != null)
  		{
  			AOrBooleanBinaryExp o = new AOrBooleanBinaryExp();
  			o.setLeft(root.clone());
  			o.setOp(new LexKeywordToken(VDMToken.OR, null));
  			o.setType(new ABooleanBasicType());
  			o.setRight(e.clone());
  			return o;
  		} else
  		{
  			return e;
  		}
  	}
docs: Chain an OR expression onto a root, or just return the new expression if the root is null. Called in a loop, this
  left-associates an OR tree.