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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 link_tail(self, node):
        '''Add a node to the tail.'''
        assert not node.head
        old_tail = self.tail

        if old_tail:
            assert old_tail.head == self
            old_tail.head = node
            node.tail = old_tail

        node.head = self
        self.tail = node