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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 get_longest_table(url='https://www.openoffice.org/dev_docs/source/file_extensions.html', header=0):
 """ Retrieve the HTML tables from a URL and return the longest DataFrame found Index(['Common and formal names', 'Membership within the UN System[a]', 'Sovereignty dispute[b]', 'Further information on status and recognition of sovereignty[d]'], dtype='object') """

    dfs = pd.read_html(url, header=header)
    return longest_table(dfs)