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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 unique_everseen(iterable, key=None):
 """ The generator to list unique elements, preserving the order. Remember all elements ever seen. This was taken from the itertools recipes. Args: iterable (:obj:`iter`):
 An iterable to process. key (:obj:`callable`):
 Optional function to run when checking elements (e.g., str.lower) Yields: The next unique element found. """


    seen = set()
    seen_add = seen.add

    if key is None:

        for element in filterfalse(seen.__contains__, iterable):

            seen_add(element)
            yield element

    else:

        for element in iterable:

            k = key(element)

            if k not in seen:

                seen_add(k)
                yield element