Trees The trees are used in ToDoLists. They are a technical feature, and fairly general, so they also can be used somewhere else.
Trees true or false The category of trees. A tree may have a content, a list of successors, a predecessor and it knows if it is a leave of a tree or not. object The content of the tree. May be any object. a list of trees Returns the list of successors of a tree. a tree or fail Returns the predecessor of a tree, or fail if there is none. a list Returns a list of leaves of the tree. a tree Returns the first successor of the tree, and adds all other successors of the tree to the tree that is returned. If the tree is a leave, it returns an empty tree. If the tree is empty, it returns the tree itself. a tree Returns an empty tree. a tree Returns a tree with argument obj. nothing Adds the [list of] tree[s] new_tree as successor to the tree tree. a list Returns a list of the contents of the trees from the leave sent up to the content of the head of the tree. a list Returns the contents of the nodes of the tree in post-order.