Last week, mysterious circles of fall leaves appeared in the Pit between Broome and Delancey, only to be dispersed by the wind and romping children. Today, the mystery was solved. Mosco, a genial LES resident and ex-graffiti artist, was sweeping leaves into perfect rings outside the M’Finda Kalunga garden and in the Rivington Street playground. He likes the idea that the circles amuse and fascinate and are ephemeral.