I don't think insert at front/back is allowed an amortized bound, it has to be flat constant. But then I don't see how libc++'s is conforming if this article is

I don't think insert at front/back is allowed an amortized bound, it has to be flat constant. But then I don't see how libc++'s is conforming if this article is true, so I'm not entirely sure what's going on there.