I am studying the Duality Chapter of Convex Optimization by Boyd. Is it possible that strong duality holds for non-convex optimization? If yes, is there any specific condition? And, what is the relationship between Slater condition and strong duality? Based on the definition in the book, the Slater condition is vague to me. I would be thankful if you can explain it. In general, what are the relationship between KKT, strong duality, Slater condition, convex and non-convex optimization?