Re: why do we need fabtoken
The paper describes fabcoin, which was just created as a benchmarking instrument for fabric.
In the paper "Hyperledger Fabric: A Distributed Operating System forAt a high level, the two approaches are not dissimilar, since they both follow a UTXO paradigm. There are several differences though, for instance fabtoken makes better use of fabric's execution model and uses a custom transaction processor instead of doing everything at the chaincode level.
In the paper after an utxo is spent, it is said that delstate isIt is as it is written - the state representing the utxo is deleted. "Labelling" the state as spent is achieved by deleting it.