Oh OK, so the zero sum is that it cost no money to either club other than administration and buy out clauses. of course there will be costs attached, call it whatever, but it looks very much like a trade as in the NFL.
I believe we will see NFL style trading moving into the market. Sanchez and Mikhataryan is the first indication that this is the way forward, places more control in the hands of clubs, marginalises (not completely) agents and keeps finances within a club. It is a more savvy way of doing business...