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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 datetime_to_timestamp(dt):
 """Convert timezone-aware `datetime` to POSIX timestamp and return seconds since UNIX epoch. Note: similar to `datetime.timestamp()` in Python 3.3+. """


    epoch = datetime.utcfromtimestamp(0).replace(tzinfo=UTC)
    return (dt - epoch).total_seconds()