OP_PAIRCOMMIT.

Would add a script command that combines two pieces of data into one fingerprint, so scripts can commit to several items at once.

Scripts, the small programs that decide who can spend coins, can easily lock coins to a single piece of data, but not to several together. OP_PAIRCOMMIT hashes two items into one and can be repeated to build trees of items. It is aimed at contracts such as delegation and Lightning Symmetry channels.