BALTIC-WAY 2007 Problem 10
We are given an table, all of whose cells may be black or white. Initially all the cells are coloured white. We may perform the following operation: choose one column or one row and change the colour of all cells in this column or row. Is it possible by repeating the operation to obtain a table with exactly black cells?
Dataset text AI-MO AoPS. Quoted with source.
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