The central bank also announced that it would purchase up to $750 billion of additional mortgage-backed securities, which lost value with the collapse of the U.S.housing market.

VOA: standard.2009.03.18

I bought a number of two-period bonds such that the value of my purchase exactly equals the proceeds that I get from shorting the one period bond, so I've made a zero wealth transaction.

我买入了一定数量的两年期债券,其成本刚好等于我卖空,一单位一年期债券获得的资金,我做的是零成本交易

耶鲁公开课 - 金融市场课程节选