def should_filter(target, stem_mapping, filtered_phrases):
    """Determine if a noun phrase should be included in the tags list.

    @param target: The noun phrase in question.
    @type target: basestring
    @param stem_mapping: Renaming of noun phrases through which target should
        be translated before tested for filtering.
    @type stem_mapping: dict (str to str)
    @param filtered_phrases: List of noun phrases to exclude.
    @type filtered_phrases: list of str
    """
    filtered = target in filtered_phrases
    filtered = filtered or stem_mapping[target] in filtered_phrases
    return filtered