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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_tissue_in_references(self, entry):
 """ get list of models.TissueInReference from XML node entry :param entry: XML node entry :return: list of :class:`pyuniprot.manager.models.TissueInReference` objects """

        tissue_in_references = []
        query = "./reference/source/tissue"
        tissues = {x.text for x in entry.iterfind(query)}

        for tissue in tissues:

            if tissue not in self.tissues:
                self.tissues[tissue] = models.TissueInReference(tissue=tissue)
            tissue_in_references.append(self.tissues[tissue])

        return tissue_in_references