def citations_versus_references(obj, citations_from_descr):
    """Given an object an a list of citations found in the description,
       return the difference between the amount of citations and external references
    """

    citations_len = len(citations_from_descr)
    ext_references_len = 0
    if obj.get('external_references'):
        ext_references_len = len(obj.get('external_references'))
    return ext_references_len - citations_len