Vocal Counting
==============

You are required to deliver the following function in :mod:`voc_module` (file :file:`voc_module.py`):

    .. py:function:: voc_count(s, sref)

such that
  
    **given**

        - *s* a non-empty :class:`str`.
        - *sref* a :class:`str` of lowercase letters.

    **returns** an :class:`int` with the number of lowercase **vocal** letters occurring in *s* that do not occur in *sref*.

For example:

    .. literalinclude:: voc_count.test
        :language: python3
        :start-after: --ini
        :end-before: --fi

Doctests are available in the :download:`voc_count.test` file.