A relation among a group of people is called a dominance relation if the associated incidence matrix A has the property that for all distinct pairs i and j, Aij = 1 if and only if Aji = 0, that is, given any two people, exactly one of them dominates (or, using the terminology of our first example, can send a message to) the other. Since A is an incidence matrix, Aii = 0 for all i. For such a relation, it can be shown (see Exercise 21) that the matrix A + A2 has a row [column] in which each entry is positive except for the diagonal entry. Prove that the matrix A + A2 has a row [column] in which each entry is positive except for the diagonal entry: 网路解答: https://imgur.com/WSTiYfw 我重写: https://imgur.com/dkYe2Wh 对网路解答做了重写，解答某些部分写得有点模糊+typo 所以不确定修改後是否是解答的原意，是否正确? 尤其是4. 谢谢 --

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