Discovered by @anon_real :
As is it possible to store box in a register (and context extension of an input), it is also possible to prove that spent box had some properties. For that, we need to issue certificate NFT during spending, to check then that corresponding box had some properties (while certificate box is not spent). Used in auctions contracts by @anon_real to get original author of NFT to pay royalty.
3 Likes