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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 _serialize_lnk(lnk):
 """Serialize a predication lnk to surface form into the SimpleMRS encoding."""

    s = ""
    if lnk is not None:
        s = '<'
        if lnk.type == Lnk.CHARSPAN:
            cfrom, cto = lnk.data
            s += ''.join([str(cfrom), ':', str(cto)])
        elif lnk.type == Lnk.CHARTSPAN:
            cfrom, cto = lnk.data
            s += ''.join([str(cfrom), '#', str(cto)])
        elif lnk.type == Lnk.TOKENS:
            s += ' '.join([str(t) for t in lnk.data])
        elif lnk.type == Lnk.EDGE:
            s += ''.join(['@', str(lnk.data)])
        s += '>'
    return s