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