5 Deposits and Withdrawals are fine. But when it comes to exchange, we need a
6 "mutually serialized" procedure with something like this:
8 (serializer-1 (serializer-2 exchange))
10 Otherwise, we are creating a "time hole" when another execution process can
11 get hold of one of the account and deposit/withdraw from it which will make
12 the end result of exchange erroneous.