Depth-first search of the tree rooted at this node.
        (First visit children, then visit current node.)

        :rtype: generator of :class:`~aeneas.tree.Tree`

def dfs(self):
        """
        Depth-first search of the tree rooted at this node.
        (First visit children, then visit current node.)

        :rtype: generator of :class:`~aeneas.tree.Tree`
        """
        for node in self.children:
            for v in node.dfs:
                yield v
        yield self