Pushing a block of ice through the streets of Mexico City, moving a mountain several inches, hiring a stripper who never quite strips: these are among Mexico City-based artist Francis Alÿs' starry-eyed projects — videos, photographs, and drawings of which are on view at the Hammer. A romantic visionary working in an indifferent world, Alÿs doesn't dwell on success or failure, but the potency of the undertaking itself.