第二句说this expected change is zero if the investor expects yield curves remain unchanged.是不是意味着如果yield curve是stable，benchmark yield就是0？rolldown return就会假设是stable，是否看到这个条件，就等同于benchmark yield是0？
是的，如果expects yield curves remain unchanged，意味着△y=0，那么根据E(△price due to the view of benchmark yield)=-duration*△y+1/2*convexity*(△y)^2，E(△price due to the view of benchmark yield)=0。
