def known_mismatch(hashes1, hashes2):
    """Returns a string if this is a known mismatch."""
    def frame_0_dup_(h1, h2):  # asymmetric version
       return ((h1[0] == h2[0]) and 
               (h1[2:] == h2[2:]) and
               (h1[1] != h2[1] and h2[1] == h1[0]))
    def frame_0_dup(h1, h2):
       return frame_0_dup_(h1, h2) or frame_0_dup_(h2, h1)
    def frame_0_missing(h1, h2):
       return (h1[1:] == h2[:-1]) or (h2[:1] == h1[:-1])
    for func in [frame_0_dup, frame_0_missing]:
       if func(hashes1, hashes2):
           return func.__name__
    return None