Where a contractual power is expressed by reference to a factual state of affairs (here, a segment 'ceasing to be' a Customer's Segment), the power can only be exercised when that factual state of affairs genuinely exists; it cannot be used merely to avoid contractual obligations while the underlying factual premise remains unchanged. The BP Refinery conditions for implied terms in fact were satisfied where a term precluding exercise of a contractual opt-out power, while the infrastructure remained necessary for the party's use, was required for business efficacy. The Court left open whether an implied term of good faith would have been breached on these facts.
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