21.   The difficulties lie in determining the characteristics of an acceptable HLA match, and in having a wide enough pool of donors to provide the matches.

22.   The difficulty does not lie in the age of the universe.

23.   The difficulty lay in proving the concept.

24.   The difficulty lies in finding and mending the millions of affected lines of code, often written decades ago.

25.   The difficulty lies in identifying the overstimulated cells.

26.   The difficulty lies in promoting male circumcision as an intervention against HIV in Africa.

27.   The difficulty lies in the way she has chosen to finance them, and her belief that her tax cuts can be carried out painlessly.

28.   The midnight agreement between Netanyahu and Arafat may have placed the peace process back on track, but more difficulties lie ahead.

29.   Their conclusion, according to NASA launch director Bob Sieck, was that the difficulty lie with an errant sensor mechanism rather than an authentic pressure problem.

30.   To be sure, some difficulty does lie ahead.