In addition, the final legislation could reduce federal mortgage interest deductions and eliminate deductions for state and local taxes. New York, New Jersey and California have families that are much more difficult than those in republican-leaning states. Any transaction can be seen as a contract between the two parties. The so-called transaction cost can be seen as the cost of the transaction contract. According to Mr Coase and others, a type of transaction costs arise from the accidental factors that occur when a deal is signed. These incidental factors may not be written into the contract due to the fact that they could not be foreseen in advance, or although they could be foreseen, they could not be written into the contract due to too many factors. Another type of transaction costs is the signing of contracts and the cost of monitoring and enforcing contracts. In economic terms, the benefits of holding any two currencies should be equal in the equilibrium of the foreign exchange market, which is: Ri=Rj (interest rate parity). Here, R stands for yield, and I and j represent currencies of different countries. If the benefits of holding two currencies are unequal, you will have A arbitrage: buy A kind of foreign exchange and sell B foreign exchange. At present, countries around the world is frequent use of interest rate leverage to implement macro-control, interest rate policy has become a central bank to control money supply and demand, and a major means of regulating economic, interest rate policy in the position in the central bank's monetary policy more and more important.