PARIS — The Forties isn’t the only decade making an impact on the runways this season. At Louis Vuitton, for example, Marc Jacobs continued an ongoing flirtation with the Eighties for fall, capturing the decade’s confidence, but coming up with a whole new way of formulating some of its best-known silhouettes. Key to the look: Slim, racy skirts and pyramid-shape tops featuring rounded shoulders and a dropped torso. Here, his belted suit. For more on the shows, see pages 6 to 9.