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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 sync_list_permissions(self):
 """ Access the sync_list_permissions :returns: twilio.rest.sync.v1.service.sync_list.sync_list_permission.SyncListPermissionList :rtype: twilio.rest.sync.v1.service.sync_list.sync_list_permission.SyncListPermissionList """

        if self._sync_list_permissions is None:
            self._sync_list_permissions = SyncListPermissionList(
                self._version,
                service_sid=self._solution['service_sid'],
                list_sid=self._solution['sid'],
            )
        return self._sync_list_permissions