Helgi Tomasson, the San Francisco Ballet’s artistic director and principal choreographer, combined elements of modern and classical ballet to create “Trio,” set to Tchaikovsky’s Souvenir de Florence. While much of the ballet recalls the aggrandized ballroom prancing one sees so often, softened arm positions and unusual footwork modernized the movements. The women’s richly autumnal-colored dresses, though shaped like a slightly less stiff version of the lampshade skirt (ballet’s frumpiest costume), were slit to the hip, and allowed a leg to swing out in many steps and kept the piece from looking as primly traditional as it might have otherwise. But […]