It's illegal, so they can't sign that as a contract, but they they can just agree to do it.

因为是违法的,合同也就无效了,不过他们可以私下达成默契

耶鲁公开课 - 博弈论课程节选

Milton makes a covenant with the reader. It's as if he's signing a contract because he's asking for credit here.

他与读者签了契约，就好像,因为他要借款所以签了份合同一样。

耶鲁公开课 - 弥尔顿课程节选

On the other hand, if we had a quarter as much venture capital, I think that would be in the sense the world would contract too much.

换句话说，如果资金数是风险资本的四分之一，我想现在订立的合同,太多了。

斯坦福公开课 - 微软CEO-Steve.Ballmer谈科技的未来课程节选