And we mean that in the best possible sense, as in Webster's: "intended to convey instruction and information as well as pleasure and entertainment." Part of NYU, the Grey Art Gallery delivers all the scholarly trappings—wall texts, erudite catalogs, lectures, symposia—for full-dress retrospectives of deserving but under-recognized artists, and for eclectic group exhibitions that put disparate movements into historical context. The former was accomplished with last year's topographical fantasias by former Army map maker Lee Mullican, who mixed Abstract Expressionist gusto with tiki-bar graphics. The latter could be discerned in "Moving Pictures," in which primitive early films were screened next to Ashcan School paintings and newspaper cartoons, revealing that all sides ripped each other off in search of a realistic and gritty modernism. A don't-miss exhibition of rarely seen paintings and drawings created in New Mexico between 1950 and '52 by that abstract master of California landscape, Richard Diebenkorn, should brighten up the Gotham winter when it opens on January 25.