The first show of this summer's free downtown concert series brings a veteran emcee with a most uncommon c.v. to the Arch. Sure, over his two-decades-long career, Chicago native Lonnie Lynn has made lots of moves expected of a rapping impresario — from the Kanye and Neptunes productions to the celebrity girlfriend (tennis star Serena Williams) and the roles in several action flicks. But Common also wrote the enduringly controversial "I Used To Love H.E.R.," which kickstarted the "Is Hip-Hop Dead?" debate way back in 1994, and he made one of the genre's most adventurous albums, 2002's unclassifiable Electric Circus. In yet another feat of unpredictability, he even donated a few verses to the Jonas Brothers.