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Published online by Cambridge University Press: 24 February 2022
Given positive numbers xj, yj such that $\sum\limits_{i = 1}^n {{x_j}} = \sum\limits_{j = 1}^n {{y_j}} $ , it can happen that $\sum\limits_{j = 1}^n {x_j^2} = \sum\limits_{j = 1}^n {y_j^2} $ : for example, $({x_j}) = (7,\,3,\,2),\,({y_j}) = (6,\,5,\,1)$ . However, such cases are exceptional.