公式：
 
　　l  Note that the options much be European-style and the puts and calls mush have the same exercise price for these relations to hold.
　　l  Fiduciary call: buy riskless bond that pays X at maturity and a call with exercise price X.
　　l  Protective put: buy security and long put.
　　l  Put-call parity 的作用：
　　ü  為option定價
　　ü  合成option。
　　ü  無風險套利。在無風險套利中，遵循long小邊，short大邊原則
　　如：
　　套利方法是， long security, long put, short call, short bonds.