thanks a lot for your fever and now two others
http://www.sciencedirect.com/science/article/pii/0016236180900290
http://www.sciencedirect.com/science/article/pii/S0378382011002591
thanks for past lecure and now is 2 others
http://www.sciencedirect.com/science/article/pii/S0166983400826263
http://www.sciencedirect.com/science/article/pii/S0016236111000275