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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 html_parts(input_string, source_path=None, destination_path=None, input_encoding='unicode', doctitle=1, initial_header_level=1):
 """ Given an input string, returns a dictionary of HTML document parts. Dictionary keys are the names of parts, and values are Unicode strings; encoding is up to the client. Parameters: - `input_string`: A multi-line text string; required. - `source_path`: Path to the source file or object. Optional, but useful for diagnostic output (system messages). - `destination_path`: Path to the file or object which will receive the output; optional. Used for determining relative paths (stylesheets, source links, etc.). - `input_encoding`: The encoding of `input_string`. If it is an encoded 8-bit string, provide the correct encoding. If it is a Unicode string, use "unicode", the default. - `doctitle`: Disable the promotion of a lone top-level section title to document title (and subsequent section title to document subtitle promotion); enabled by default. - `initial_header_level`: The initial level for header elements (e.g. 1 for "<h1>"). """

    overrides = {
        'input_encoding': input_encoding,
        'doctitle_xform': doctitle,
        'initial_header_level': initial_header_level,
        'report_level': 5
    }

    parts = core.publish_parts(
        source=input_string, source_path=source_path,
        destination_path=destination_path,
        writer_name='html', settings_overrides=overrides)
    return parts