At long last, the Second Avenue subway has opened in New York City (at least phase I)—a source of great relief for overburdened riders, who can enjoy what is now New York State’s largest permanent public art installation. At the 86th Street stop, one  of four on the new line operating on the Upper East Side, photographer and painter Chuck Close has created 12 nine-foot mosaics, one of them acknowledging friend and artist Kara Walker, who is the Tepper Chair in Visual Arts at Mason Gross School  of the Arts.