That's an easy one, yes.
The interesting proposal by the IMF a few years ago.... I'll get my acronyms wrong; it might have been the so-called fat taxes, as you were referencing. But related to taxes on wholesale borrowing by banks, it was to reduce the incentive for banks to borrow in the capital markets, because that borrowing creates a risk to the system as a whole. It creates a negative externality. It makes them too big to fail and it causes the types of crises that we saw. The issue was, well, could you use tax policy to reduce that?
What the regulatory community has done is to use regulation instead of tax policy to do it, in part because of the arbitrage issues I talked about earlier, which suggests...and part of that judgment was based on the ability to evade a tax by changing an instrument slightly or borrowing in a different subsidiary, etc., not having a global approach. I wouldn't recommend it as a good revenue generator.
Am I out of time to answer? Because I was so close to answering what is most efficient....