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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def infer(msg, mrar=False):
 """Estimate the most likely BDS code of an message. Args: msg (String):
 28 bytes hexadecimal message string mrar (bool):
 Also infer MRAR (BDS 44) and MHR (BDS 45). Defaults to False. Returns: String or None: BDS version, or possible versions, or None if nothing matches. """

    df = common.df(msg)

    if common.allzeros(msg):
        return 'EMPTY'

    # For ADS-B / Mode-S extended squitter
    if df == 17:
        tc = common.typecode(msg)

        if 1 <= tc <= 4:
            return 'BDS08'  # indentification and category
        if 5 <= tc <= 8:
            return 'BDS06'  # surface movement
        if 9 <= tc <= 18:
            return 'BDS05'  # airborne position, baro-alt
        if tc == 19:
            return 'BDS09'  # airborne velocity
        if 20 <= tc <= 22:
            return 'BDS05'  # airborne position, gnss-alt
        if tc == 28:
            return 'BDS61'  # aircraft status
        if tc == 29:
            return 'BDS62'  # target state and status
        if tc == 31:
            return 'BDS65'  # operational status

    # For Comm-B replies
    IS10 = bds10.is10(msg)
    IS17 = bds17.is17(msg)
    IS20 = bds20.is20(msg)
    IS30 = bds30.is30(msg)
    IS40 = bds40.is40(msg)
    IS50 = bds50.is50(msg)
    IS60 = bds60.is60(msg)
    IS44 = bds44.is44(msg)
    IS45 = bds45.is45(msg)

    if mrar:
        allbds = np.array(["BDS10", "BDS17", "BDS20", "BDS30", "BDS40",
                           "BDS44", "BDS45", "BDS50", "BDS60"])
        mask = [IS10, IS17, IS20, IS30, IS40, IS44, IS45, IS50, IS60]
    else:
        allbds = np.array(["BDS10", "BDS17", "BDS20", "BDS30", "BDS40",
                           "BDS50", "BDS60"])
        mask = [IS10, IS17, IS20, IS30, IS40, IS50, IS60]

    bds = ','.join(sorted(allbds[mask]))

    if len(bds) == 0:
        return None
    else:
        return bds