Sotheby’s modern sale on Tuesday night opened with aggressive bidding. A Los Angeles art advisor competed with three other bidders for a Jean Arp sculpture that eventually sold to another woman in the room for almost two and a half times the estimate. Beaumont Nathan’s Emma Lasry bid on a colorful Robert Delaunay still life that was bid up over the estimate range. There were four bidders on František Kupka’s Flux et reflux, even though it was backed by an irrevocable bid. It ended up selling for a price well above Joseph Hazen’s other Kupka work, despite the fact that that one had an estimate that was 66 percent higher. Hazen’s Giacometti, Femme debout (Poseuse I), sold for a price 40 percent above the estimate.