By "users" I simply mean people who use the system. While you cannot know what user knows what address, and not every address maps to a single user, nevertheless there are people using it.


The old transactions would still be there, there would just be one more transaction type.

Essentially, the idea allows you to say: "I promise not to double spend the input of this transaction. If you catch me doing it, please pay this large fee to the miner."