In this paper we introduce the notion of (f,ω)-compatible pair (B,H), by which we construct a Hopf algebra in the category HHYD of Yetter-Drinfeld H-modules by
<正>The passing of Kai Lai Chung () on 1 June 2009 at the venerable age of 91 reminds me forcibly of the importance of Chung’s work in my own life. Chung posed