Fools born after 1970 think westerns began and ended with Unforgiven, but there would be no Unforgiven—hell, there'd be no Clint Eastwood—without Liberty Valance's bracing ambiguity. Three of the greatest movie actors of all time push each other to some of the finest work of their careers, with John Wayne and Jimmy Stewart playing against type as an oaf and a coward, respectively, and the always-brilliant Lee Marvin at his evilest. (Grand Illusion, 1403 NE 50th St, 523-3935. 6:30 and 8:45 pm, $8.)