def OR(a, b):
    """
    Returns a single character '0' or '1'
    representing the logical OR of bit a and bit b (which are each '0' or '1')
    
    >>> OR('0', '0')
    '0'
    >>> OR('0', '1')
    '1'
    >>> OR('1', '0')
    '1'
    >>> OR('1', '1')
    '1'
    
    """
    if a == '0' and b == '0':
        return '0'
    
    return '1'