Can something pilfered from high school geometry class be chic? You bet. The recent collections offered plenty of examples, from stylish checks and grids to pyramids and polkadots. Marni’s Consuelo Castiglioni, for instance, served up a festive medley of patterns with cartoonish charm, while Dries Van Noten and Sabyasachi Mukherjee took those exacting shapes for a dazzling op-art spin. Accessories got graphic too, right down to Yves Saint Laurent’s edgy cutout booties.