“…The following theorem (Theorem ) indicates the production points of the optimal solution. The proof of Theorem 1 has been shown in our previous work (Zhang et al., ). Theorem For the (i + 1, j)‐problem with mod(U, W) = 0, either - there exists an optimal production plan such that for any t (), if
then , and if there exists some m such that then for some n (n = 1, 2, …, U/W), or - (2) there exists some k () such that
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