MILAN — Sexy and sober: Leave it to Miuccia Prada to combine the two. In the Prada collection she showed on Monday, she continued last season’s flirtation with the waist, marking it with cummerbunds or showing flashes of bare midriff, like those peeking out from her tiny cropped sweaters. Provocative? Well…yes and no. Here, her racy little V-neck and considerably more modest pleated skirt. For more on Milan, see pages 4 to 7.