3. The transmission system operator shall implement and publish non-discriminatory and transparent congestion-management procedures which facilitate cross-border exchanges in natural gas on a non-discriminatory basis and which shall be based on the following principles:
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(a)
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in the event of contractual congestion, the transmission system operator shall offer unused capacity on the primary market at least on a day-ahead and interruptible basis; and
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(b)
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network users may re-sell or sublet their unused contracted capacity on the secondary market.
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As regards the first subparagraph, point (a), a Member State may require notification or information of the transmission system operator by network users.