If bS ði þ b þ hÞC > 0, we can get (6) holds if and only if ðT t1Þ < 0. It is a contradiction, because
by assumption, we have t1 6T . Similarly, if bS ði þ b þ hÞC ¼ 0, then, from (6), we obtain T ¼ t1.
Substituting this into (7), we get A ¼ 0, which is contradictory, because the ordering cost per cycle, A, is
positive. Therefore, if bS ði þ b þ hÞCP0, the optimal solution of Pðt1; T Þ does not exist