General Fonseka,in the letter, says Sri Lanka asked India on October 15 to place troops on alert in case they would be needed to intervene to foil a coup on the island.

VOA: standard.2009.11.14

And, in this case, they had foil that was less than a micrometer thick.

这样的话，他们采用的箔的厚度小于一微米。

麻省理工公开课 - 固态化学导论课程节选

Hobbes was in many ways a perfect foil for Machiavelli.

霍布斯，从很多方面来说,他都是马基雅维利的完美配合。

耶鲁公开课 - 政治哲学导论课程节选