I hope you don't mind me bringing up old threads, how it's just too cool.

The [Lambek–Moser theorem](https://en.wikipedia.org/wiki/Lambek–Moser_theorem) is very much a theorem about left and right adjoints applied to the natural numbers (\\(\mathbb{N}\\)), though in the literature, it seems no one has noticed this.

What's neat is that the adjoints partition the natural numbers.