ASU 004 All Soviet Union MO 1961 8.4 stars in a table
Source:
June 17, 2019
combinatoricssquare table
Problem Statement
Given a table . a) Find, how stars can be put in its fields in such a way, that erasing of two arbitrary lines and two columns will always leave at list one of the stars. b) Prove that if there are less than stars, You can always find two columns and two rows, such, that if you erase them, no star will remain in the table.