def expectation_value(first_fencer, second_fencer):
    """Returns the expected winning value of the first given fencer in a bout
    with the second.  The winning value is actually the fraction of won single
    points.  I.e., an expectation value of 0.7 means that the first fencer will
    make 70% of the points.

    :Parameters:
      - `first_fencer`: first fencer, for whom the expectation value is to be
        calculated
      - `second_fencer`: second fencer, opponent in the bout

    :type first_fencer: Fencer
    :type second_fencer: Fencer

    :Return:
      - expected winning value, with 0 S{<=} value S{<=} 1.

    :rtype: float
    """
    return 1 / (1 + 10**((second_fencer.felo_rating_exact - first_fencer.felo_rating_exact)/400.0))