The Open Cage Ensemble makes some good choices in its revival of Steve Martin's thinking-man's comedy. This year marks the 50th anniversary of Einstein's death and the centenary of his most significant papers. And the production takes place in a bar: Martin imagines Picasso and Einstein meeting in a Paris bistro, where he contrasts their obsessions with those of various barflies. Abounding with delightful if sometimes anachronistic epiphanies about physics, art, and love, this 75-minute romp bubbles over with the optimism of its turn-of-the-century setting. High-spirited yet plausible, Danyel Read's staging boasts inspired casting, especially Joel Ewing and Chad Reinhart as the two happily human 20th-century icons. Especially effective are the slide projections, by tech director Matt Reese among others, on the bar's TV monitors: playfully particular, they animate Martin's observations on art and life in this feast of reason. Through 5/28: Thu-Sat 8 PM. Town Hall Pub, 3340 N. Halsted, 773-525-1668. $15.