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magnificent rectangular board, with a symbol in each sqaure

Source: Portugal OPM 2023 p6

May 15, 2024
combinatoricscombinatorial geometry

Problem Statement

A rectangular board, where in each square there is a symbol, is said to be magnificent if, for each lineL L and for each pair of columns CC and DD, there is on the board another line MM exactly equal to LL, except in columns CC and DD, where MM has symbols different from those of LL. What is the smallest possible number of rows on a magnificent board with 20232023 columns?