I recently learnt of these remarkable combinatorial objects from @numberphile https://youtu.be/0mXz-NP-raY
They must be among the more amazing things to be counted by the Catalan numbers.
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Huh. I have that book, but I must have overlooked this section. It’s so dense with wonderful things.
Thanks. Twitter will use this to make your timeline better. UndoUndo
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