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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 del_reference(self, source, target, **kwargs):
 """Remove existing reference """

        rc = api.get_tool("reference_catalog")
        uid = api.get_uid(target)
        rc.deleteReference(source, uid, self.relationship)
        # unlink the version of the reference
        self.link_version(source, target)