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.

Category: LAW 
Clue: In Latin legal lingo it means "by the fact itself"
ipso facto

Category: I GOT 3 As, MOM! 
Clue: In legend, this pure knight found the Holy Grail
galahad

Category: ARCHITECTURE 
Clue: This architecturally controversial Paris complex opened in 1977

pompidou centre/beaubourg