Both opening Saturday: Few artists will boast even passing acquaintance with the mathematical concept of “Set Theory,” let alone create a large painting in homage to Georg Cantor, the theory’s founder. In his “Song for Georg,” Minnesota painter Jim Dryden uses abstract gestures in various tones and shapes to honor Cantor. Dryden’s “Set Theory I” is shown here. (5-8 p.m. Sat., free opening reception, Form + Content, 210 N. 2nd St., Mpls. Ends Oct. 26. 612-436-1151 or Also opening at nearby Circa Gallery is a show by Kenneth Steinbach, who draws topographical maps on piano keys, preserves other drawings in resin, and carves designs into old chalkboards. (210 N. 1st St., Mpls. Ends Nov. 3. 612-332-2386 or