Maximum Presufix
================

We define *presufix* of ``s`` as a string such that is both prefix and sufix of ``s``.
Any ``s`` might have several presufix and we are interested in the one with maximum length that is not equal to ``s``: the **maxpresufix**.
For instance, ``'a'`` and ``'abba'`` are both presufix of ``'abbabba'``, being the later the longest one.

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

    .. py:function:: maxpresufix(n)

such that

    **given** *n*, a non-empty :class:`str` of lowercase letters.

    **returns** a :class:`str` with either the *maxpresufix* of ``s`` if it exists, or the empty string otherwise.

For example:

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

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