11.   Weapons sites proved enormously difficult to destroy during the gulf war, said several post-war studies.

12.   Casting the other principal roles proved more difficult.

13.   Choosing between Ms. Binford and Ms. Coyoc proves more difficult.

14.   Creating a truly unified nation has proven more difficult.

15.   Cracking down on unruly regional leaders has proven more difficult.

16.   Dismantling the other six, inhabited by a few militants, may prove more difficult.

17.   Escaping racial stereotyping, however, proved difficult in Washington, where there were few black Republicans.

18.   Getting the balance of money from Congress, however, could prove more difficult.

19.   Her efforts could also prove more difficult now, because the first batch of contributions is often the easiest to take in, political experts say.

20.   Other mergers could prove more difficult.