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MathNet 2023-part-06 — 191 problems (EN–VI) Question 144

Math Olympiad Vault · MathNet 2023-part-06 — 191 problems (EN–VI)

Question 144

Let $\mathcal{S}$ be a family of $n$ sets, each of size $k$, such that $A \Delta B \in \mathcal{S}$ whenever $A, B \in \mathcal{S}, A \neq B$.

a) Is it possible that $n = 2023$? If it is, find all possible values of $k$.

b) Is it possible that $n = 1023$? If it is, find all possible values of $k$.

Notation: $A \Delta B = (A \setminus B) \cup (B \setminus A)$.