def norm(appearances, year, MAX_YR=2013):
    """
    Returns number of appearances per year.
    
    Parameters:
    ------
    appearances: (float)
    the number of appearances of the character
    
    year: (float)
    the year of its first appearance
    
    Keyword arguments:
    ------
    MAX_YR: (float)
    year boundary for the source data
    
    Returns:
    ------
    appearances_per_yr: (float)
    the number of appearances per year for each character
    
    Examples:
    ------
    norm(10, 2004) = 1
    """
    if year == year and appearances == appearances:
        appearances_per_yr = appearances/(MAX_YR - year + 1)
        return appearances_per_yr
    else:
        return