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Plant tree on tabular grid

Source: Vietnam Mathematical Olympiad 2016, Day 1, Problem 4

January 6, 2016
combinatorics proposedcombinatorics

Problem Statement

Let mm and nn be positive integers. A people planted two kind of different trees on a plot tabular grid size m×n m \times n (each square plant one tree.) A plant called inpressive if two conditions following conditions are met simultaneously: i) The number of trees in each of kind is equal; ii) In each row the number of tree of each kind is diffrenent not less than a half of number of cells on that row and In each colum the number of tree of each kind is diffrenent not less than a half of number of cells on that colum.
a) Find an inpressive plant when m=n=2016m=n=2016; b) Prove that if there at least a inpressive plant then 4m4|m and 4n4|n.