Difficult abstraction with sets
Source: European Mathematical Cup 2022, Junior Division, Problem 4
December 19, 2022
combinatoricsSetsintersections
Problem Statement
A collection of distinct (not necessarily non-empty) subsets of is lovely if for any three (not necessarily distinct) sets , and in at most three out of the following eight sets are non-empty
\begin{align*}A \cap B \cap C, \ \ \ \overline{A} \cap B \cap C, \ \ \ A \cap \overline{B} \cap C, \ \ \ A \cap B \cap \overline{C}, \\ \overline{A} \cap \overline{B} \cap C, \ \ \ \overline{A} \cap B \cap \overline {C}, \ \ \ A \cap \overline{B} \cap \overline{C}, \ \ \ \overline{A} \cap \overline{B} \cap \overline{C}
\end{align*}
where denotes the set of all elements of which are not in . What is the greatest possible number of sets in a lovely collection?