PARIS — Helmut Lang made a welcome return to the City of Light and the runway this season. His spring collection was full of beautiful variations on the striking city clothes he has made his own. There were great coats, of course, worn over skinny pants, web-like string knits and plenty of pieces featuring the straps and strips he uses to dress things up. Lang’s new favorite fastening: the zipper. Here, one of his fab short chiffon dresses, in bold contrasting tones. For more, see pages 4 and 5.