He said officials have discovered a number of plots in recent months involving "homegrown extremists."

VOA: special.2009.10.17

As you have discovered in recent problem set, it is possible to construct all subsets of a set.

正如你在最近的问题集中发现的，构建集合的所有子集是可行的。

麻省理工公开课 - 计算机科学及编程导论课程节选