This tag is for questions asking for combinatorial structures of maximum or minimum possible size under some constraints. Typical questions ask for bounds or the exact value of the extremal size, or for the structure of extremal configurations.

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Lower bound for the chromatic number of $\mathbb{R}^n$

I'm going through a proof that of the following lower bound for the chromatic number of $\mathbb{R}^n$: $$\chi(\mathbb{R}^n) \geq (1.2 + o(1))^n$$ At some point in the proof we get that ...