One strike against this data structure is that it can contain gaps: observe the empty() node between the nodes labeled 4 and 6. Another strike is that it is resistant to a straightforward notion of breadth and depth. The nodes are labeled 1-6 (skipping an empty node where one might expect a 5) in some sort of order. Is that order breadth-first, depth-first, or arbitrary? The answer depends on whether you consider the trees in forests to be siblings or whether you consider each node of a forest as a binary fork in a tree.
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Умер один из основателей «Эха Москвы»Умер один из основателей «Эха Москвы» Сергей Игнатов
if (key is null)
It seems that the ideal solution would be to push the burden of correctness outward, while still enforcing the correctness checks. How can we do that? Well, with types of course!