[lemma=and] [tag=NNP] [tag=NNP] □
[lemma=and] [tag=NNP] [tag=NNP] □ □
[lemma=and] [tag=NNP] [tag=NNP] (□ | □)
It can be difficult to earn a living with this approach , and many countries , particularly those in Western Europe and East Asia , have restrictive employment and visa policies . Two of the housing GSEs , Fannie Mae and Freddie Mac , have played a critical role in establishing a nationwide secondary mortgage market and increasing efficiency through greater standardization of mortgage products . Others , including Jeffrey Skilling and Kenneth Lay , have been indicted and still await trial . Recently , two of his doctoral students , David Koller and Natasha Gelfand , have started to develop algorithms to do the job .