(In python) Write a function BUtify(s) that takes as input an arbitrary string s and uses recursion to determine and return a new string in which all lower-case bs are replaced by upper-case Bs and all lower-case us are replaced by upper-case Us. For example:

>>> BUtify('you be you') result: 'yoU Be yoU' >>> BUtify('beautiful') result: 'BeaUtifUl' >>> BUtify('unbelievable') result: 'UnBelievaBle'