MathDB

Consider a

m*n

board. On each box there's a non-negative integrer number assigned. An operation consists on choosing any two boxes with

1

side in common, and add to this

2

numbers the same integrer number (it can be negative), so that both results are non-negatives. What conditions must be satisfied initially on the assignment of the boxes, in order to have, after some operations, the number

0

on every box?.

Problem Statement