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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 normalize_fulltext(fulltext):
 """Return a 'cleaned' version of the output provided by pdftotext."""

    # We recognize keywords by the spaces. We need these to match the
    # first and last words of the document.
    fulltext = " " + fulltext + " "

    # Replace some weird unicode characters.
    fulltext = replace_undesirable_characters(fulltext)
    # Replace the greek characters by their name.
    fulltext = _replace_greek_characters(fulltext)

    washing_regex = get_washing_regex()

    # Apply the regular expressions to the fulltext.
    for regex, replacement in washing_regex:
        fulltext = regex.sub(replacement, fulltext)

    return fulltext