TASK DEFINITION: You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.
PROBLEM: Category: MATHLETES 
Clue: John Nash has a beautiful mind that contributed to this "theory" of strategic decision making

SOLUTION: game theory

PROBLEM: Category: WORLD GEOGRAPHY 
Clue: This capital city is situated in the Judean Hills

SOLUTION: jerusalem

PROBLEM: Category: U.N. SECRETARIES-GENERAL 
Clue: He served in the German army, years not entirely clear

SOLUTION:
waldheim