Any provision of the agreement of merger or consolidation adopted pursuant to this subsection (a) may be made dependent upon facts (including, but not limited to, the occurrence of any event, including a determination or action by any person or body, including the corporation) ascertainable outside of such agreement, provided that the manner in which such facts shall operate upon the terms of the agreement is clearly and expressly set forth in the agreement of merger or consolidation.
8 Del. C. § 261